I dedicate this thesis to my family but especially to my son Fabrice.

You must remember that even the sky is not the limit… Your mum …

Abstract

Carbonaceous meteorites are the most primitive objects of the solar system. They contain up to 4% of carbon, mainly occurring as insoluble organic matter (IOM). This IOM contains key information about the organo-synthesis processes taking place in the Solar System, which are so far poorly understood. A statistical model was recently proposed for the IOM molecular structure along with a possible synthesis pathway for its hydrocarbon backbone [START_REF] Derenne | Model of molecular structure of the insoluble organic matter isolated from Murchison meteorite[END_REF].

The first aim of this work was to test experimentally this pathway using an organic plasma as a source of CHx radicals. This device allowed the formation of both soluble and insoluble OM. The IOM was analyzed through the same techniques as those previously used for the chondritic IOM, revealing numerous similarities between both materials and thus supporting the proposed pathway. Moreover, NanoSIMS analyses revealed large isotopic variations at a sub-micrometric spatial resolution that are commensurable with those observed in chondritic IOM.

Then, the source of heteroatoms (N and O) into the IOM was experimentally investigated through the addition of heteroelement-containing precursors to the hydrocarbonaceous radicals. As for nitrogen, two types of precursors were considered: hexylamine as a source of nitrogen hydrides and N 2 . Although both precursors led to nitrogen incorporation in the IOM, nitrogen hydrides seem to be more relevant based on the nitrogen speciation. Two types of experiments were performed to investigate the potential source of oxygen in the chondritic IOM. They were designed to address the two main scenarios proposed in the literature to account for the origin of the oxygen in the chondritic IOM: either aqueous alteration on the asteroidal parent body or O incorporation during the organo-synthesis in the primitive solar nebula. When the aqueous alteration is mimicked, the chemical composition of the SOM and IOM makes this pathway a reasonable source of the chondrite oxygen moieties. In contrast, no evidence for direct incorporation of O from OH radicals could be brought.

Résume

Les météorites carbonées sont les objets les plus primitifs du système solaire. Ils contiennent jusqu'à 4 % de carbone, principalement présent sous forme de matière organique insoluble (MOI). Celle-ci contient des informations essentielles sur les processus d'organo-synthèse qui se déroulent dans le système solaire, qui sont jusqu'ici mal compris. Un modèle statistique a été récemment proposé pour la structure moléculaire de la MOI ainsi qu'une voie de synthèse possible pour le squelette hydrocarboné de cette macromolécule [START_REF] Derenne | Model of molecular structure of the insoluble organic matter isolated from Murchison meteorite[END_REF].

Le premier objectif de ce travail était de tester expérimentalement cette voie avec un plasma organique comme source de radicaux CHx. Ce dispositif a permis la formation de matière organique soluble et insoluble. La MOI a été analysée par les mêmes techniques que celles utilisées précédemment pour la MOI chondritique, révélant de nombreuses similitudes entre les deux matériaux et validant le mécanisme proposé. En outre, des analyses NanoSIMS ont révélé, à une résolution spatiale sub-micrométrique, de grandes variations isotopiques qui sont du même ordre de grandeur que celles observées dans la MOI chondritique.

Ensuite, la source des hétéroatomes (N et O) dans la MOI a été expérimentalement étudiée en ajoutant des précurseurs contenant des heteroelements aux radicaux hydrocarbonés. En ce qui concerne l'azote, deux types de précurseurs ont été considérés : l'hexylamine comme source d'hydrures et l'azote moléculaire N 2 . Bien que les deux précurseurs conduisent à l'incorporation d'azote dans la MOI, les hydrures d'azote semblent être plus pertinents, d'après la nature des fonctions azotées formées. Deux types d'expériences ont été effectuées afin d'étudier la source potentielle d'oxygène dans la MOI chondritique. Elles ont été conçues pour tester les deux principaux scénarios proposés pour rendre compte de la présence d'oxygène dans la MOI chondritique : soit l'altération aqueuse sur le corps parent ou l'incorporation d'oxygène pendant l'organosynthèse dans la nébuleuse solaire primitive. Lors de l'expérience simulant l'altération aqueuse, la composition chimique de la matière organique soluble et insoluble est en accord avec ce qui est observé dans la matière organique des météorites. En revanche, aucun élément en faveur de l'incorporation directe d'oxygène par des radicaux OH n'a pu être apporté.

Introduction Introduction

Meteorites, more precisely carbonaceous chondrites preserving a record of the chemistry that occurred in the early Solar System, strongly contribute to the knowledge which up to these days has been established.

One of the most studied class of meteorites in the research area are carbonaceous chondrites such as Murchison and Orgueil. They are amongst the most primitive form of meteorites, but they are also the most chemically complex.

They contain a plethora of organic molecules which are divided into two fractions.

The first one being the soluble part which is simply extracted by dissolving in common organic solvents. This matter includes a number of molecules of biological interest, such as acids or sugars. This fraction has been intensely studied and a great amount of molecular and isotopic data is available. The second fraction, insoluble, is equivalent to kerogen in terrestrial rocks. The chemical and physical properties of insoluble organic matter are less well known which causes a poor understanding of the organic synthesis process which took place in the solar system. That is why the aim of this work is to put forward the synthesis pathway under similar conditions yjzy may have occurred during the solar system formation. The laboratory work is based on the statistical model of the molecular structure of the insoluble organic matter which has been investigated by Derenne and Robert previously (Derenne and Robert 2010). Afterwards, the products are characterized using several techniques and the same set of techniques used for meteorites. There are spectroscopic instruments such as Fourier transform infrared spectroscopy, solid state nuclear magnetic resonance and electron paramagnetic resonance along with chemical and thermal degradation and high resolution transmission electron microscopy. Additionally, NanoSIMS analysis is performed in order to describe the isotopic character of produced materials. The ambition of this work is to improve our understanding of the chemical structure of the IOM isolated from primitive meteorites and mainly to improve our perception of the organic synthesis which took place in the early solar system. This thesis consists of six parts. First of all, the chapter "State of the Art" presents the knowledge which is established in regards to: (1) organics in the space, (2) theories of the origin of our Solar System and (3) meteorites and data on syntheses of analogues of extraterrestrial organic reported so far. Subsequent chapter includes a short description of analytical techniques and protocols used to characterize obtained organic matters along with the synthesis device. The third chapter refers to the laboratory synthesis of organic matter in a plasma discharge of short n-alkanes chains under vacuum. These initial results show that organic matter containing only atoms of carbon and hydrogen could be synthesized through our apparatus. In the next chapter, I describe results about attempts to integrate oxygen into the IOM.

Finally, syntheses with nitrogen-containing precursors in order to incorporate this heteroelement are reported. Conclusion and the final thoughts on the perspective of this work are presented in the last section.

State of the art

Meteorites

Meteorites fell down on the planet Earth long time ago, well before people started observing them. As far back as 650 B.C., two independent events were recorded in ancient chronicles from China and Greece, also some time before, in 1478 B.C. a fall of meteorites was reported on the grounds of Crete. In the old days, ancient people considered meteorite falls of religious significance and no one could really find any explanation as to where they come from and what they are. Finally, in 1794, Chladni, a German physicist and lawyer, was the first scientist to publish a book where he claimed that meteorites are extraterrestrial bodies travelling from space at a high speed passing the atmosphere. His idea about iron masses [START_REF] Marvin | Ernst Florens Friedrich Chladni (1756-1827) and the origins of modern meteorite research[END_REF] did not convince the community but Biot a young French scientist, persuaded the public with the finding of l'Aigle meteorite from Normandie in 1803 [START_REF] Gounelle | The Meteorite Fall at l'Aigle on April 26th 1803 and the Biot Report[END_REF]. This moment was the crucial breakthrough and since then, the science of meteorites was launched.

Meteorites -precious extraterrestial bodies

Our solar system which consists of the Sun -our star, eight planets and their natural satellites, dwarf planets, asteroids and comets, is located in an outward spiral arm of the Milky Way galaxy. The planets, which travel in orbit around the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The planets were formed as a by-product of the birth of the sun around 4.5 billion years ago. There are over 100 billion stars like our sun in our galaxy, so could there be other planets like the Earth? More than 200 years ago, our knowledge about our Solar System was already developed, nevertheless there are still many unanswered questions which puzzle many scientists. This is why meteorite research is one of these fields, which is essential to our understanding of the origin and early history of the solar system. The study of meteorites, their chemical and isotopic compositions, can determine from which part of the solar system they came from, how long they have been in space for and what is their age since their formation.

Meteorites are natural objects that survive their fall to Earth from space. Before passing the Earth's atmosphere, their fragments are known as meteoroids. Other extraterrestrial materials include interplanetary dust particles (IDPs) collected in the stratosphere and in polar ices. Most of meteorites and IDPs are fragments of asteroids or comets but some come from the Moon and others are Martian. Meteorite research provides a chronology of the first 100 million years of the Solar System history and gives evidence that our Sun went through a highly radiative, T Tauri stage. They are assigned to groups on the basis of their contents [START_REF] Simkiss | Meteorites: The Key to our Existence[END_REF].

Exfoliating from a larger extraterrestrial body, these individual pieces can range in size from tiny grains of dust to large bodies, several meters in diameter. Captured by the Earth's gravitational force, they are accelerated to speeds over 10 kilometers per second. As they enter Earth's thick gaseous atmosphere they rapidly slow down due to the friction with the atmosphere and glow, flashing across the sky, before finally crashing onto the ground [START_REF] Smith | Meteorites. Firefly Books[END_REF].

Meteorites are divided into two groups depending if the fall was observedfalls, or notfinds. Each meteorite is given a name based on the locality or geographical characteristics near their point of recovery and recorded on existing topographic maps. When they are found in Antarctica and the desert of Australia or northern Africa, they are given names and numbers because a large number of samples originate from the same location. Fragments considered to be from the same meteorite fall, which, in Antarctica or hot deserts, might have different numbers or even names because they were found in different locations, are called "paired."

Up to these days, more than 40,000 meteorites are currently known. This number is quickly growing through the discovery of large concentrations of meteorites in the cold and hot deserts [START_REF] Davis | Meteorites, Comets, and Planets: Treatise on Geochemistry[END_REF]. Finally, recent rules do not allow a meteorite to be named after a person, nevertheless, a few names survived.

Meteorite classification

Up to these days there are currently about 40,000 meteorites classified in the collections worldwide. Based on their bulk compositions and textures, meteorites can be divided into two main categories: chondrites and non-chondritic meteorites (Fig. 1.1). Moreover, they are allocated into groups depending on their chemistry, mineralogy and petrography [START_REF] Davis | Meteorites, Comets, and Planets: Treatise on Geochemistry[END_REF]. The aim of this classification is to gather meteorites in families in order to find their formation histories and discover possible links between them. Fig. 1.1 Classification of meteorites [START_REF] Davis | Meteorites, Comets, and Planets: Treatise on Geochemistry[END_REF] Most irons, stony-irons and achondrites come from differentiated parent bodies which experienced largescale partial melting, isotopic homogenization and subsequent differentiation thus explaining the lack of chondritic textures in these meteorites. On the contrary, primitive meteorites were not modified due to melting or differentiation of the parent body hence they are called chondrites, as most of them comprehend small, spherical, igneous inclusions-chondrules, which solidified from melt droplets. In addition, chondrites (> 70 % of known meteorites, Hutchison, R.

2004) consist of three other components: FeNi-metal, refractory Ca-Al-rich inclusions (CAIs) and fine-grained matrix material. It has to be noted that apart from the most volatile elements, the composition of all chondrites is remarkably similar to that of solar photosphere (Fig. 1.2). They comprise of a material, which was formed directly from the solar nebula, and surviving interstellar grains were in some cases modified by aqueous and thermal processes. Thus, meteorites are easier specimens to analyze and they provide the best estimates for mean abundances of condensable elements in the Solar System. Fig. 1.2 The abundance of elements in the Sun's photosphere plotted against their abundance in the Allende CV3 chondrite. Most elements lie very close to the curve of equal abundance (normalized to silicon). Several volatile elements lie above the curve, presumably because they are depleted in meteorites (rather than being enriched in the Sun), while only lithium lies substantially below the curve; lithium is depleted in the solar photosphere because it is destroyed by nuclear reactions near the base of the Sun's convective zone (de Pater and Lissauer 2015)

The carbonaceous chondrites, the object of interest of my thesis, are further classified according to their primary and secondary characteristics. The primary classification (CI, CM, CR, CO, CB, CH, CV, and CK) reflects the original properties of the meteorites such as bulk chemistry and mineralogy. Each group has a unique and well-defined elemental abundance pattern. The secondary classification reflects petrographic type which indicates the extent and type of alteration that the meteorite has undergone on its parent body. According to the guide which has been introduced by Van Schmus and Wood in 1967, chondrites are divided into 6 groups where the degree of thermal and aqueous alteration is described. For instance, type 1 and 2 chondrites are meteorites which experienced extensive aqueous alteration [START_REF] Mcsween | Meteorites and Their Parent Planets[END_REF] to the point that most of olivine and pyroxene have been altered to hydrous phasein case of type 1. The alteration took place in the temperature range between 20-150°C. The maximum temperature is high but not sufficient to induce thermal metamorphism. Type 3 chondrites are considered as the least altered meteorites. They are often called unequilibrated as the minerals present in their structure show a wide range of composition. In contrast, equilibrated meteorites, which belong to types 4 to 6, show an increasing degree of chemical equilibrium and textural recrystallization due to high temperature. It is important to mention that this scheme cannot be applied to all meteorite species as in some cases such as several CI and CM chondrites, aqueous alteration is followed by thermal metamorphism (Kimura andIkeda 1992, Tonui et al. 2014).

Chondrites as the witnesses of the formation of the Solar system

The study of the chondrites bulk composition helps to understand current concepts of how the Solar System formed. For instance the chondritic bulk structure varies and the differences are attributed to the volatilities of the constituting elements.

The fractionation of highly volatile species relates to the formation of chondritic components from vapor. No chondrites except the CI group formed with a full, solar complement of volatile elements and the level of depletion corresponds to the degree of volatility, where the most volatile elements are most depleted. In general, the gradual depletion trend with increasing volatility is observed in primitive chondrites (Fig. 1.3). When metallic iron is plotted versus oxidized iron (Fig. 1.4), the solar total iron is situated diagonally towards oxidation. All chondrites fall well below the line, indicating loss of iron. Thus, depletion of nickel and other siderophile elements shows that the lost iron was rather metallic than oxidized.

Apart from depletion of volatiles and metals, there is another aspect, such as isotopic anomalies, which connects meteorites with the occurring chemistry of the early solar system. It is clear that meteorites contain preserved interstellar and circumstellar molecular materials but the data from isotopic ratios of present elements like hydrogen [START_REF] Robert | The concentration and isotopic composition of hydrogen, carbon and nitrogen in carbonaceous meteorites[END_REF][START_REF] Kolodny | Deuterium in carbonaceous chondrites[END_REF][START_REF] Remusat | The insoluble organic matter in carbonaceous chondrites: Chemical structure, isotopic composition and origin[END_REF] , carbon [START_REF] Sephton | Small-scale hydrous pyrolysis of macromolecular material in meteorites[END_REF][START_REF] Smith | Endogenous Carbon in Carbonaceous Meteorites[END_REF][START_REF] Sephton | Aromatic moieties in meteoritic macromolecular materials: analyses by hydrous pyrolysis and δ13C of individual compounds[END_REF], nitrogen [START_REF] Robert | The concentration and isotopic composition of hydrogen, carbon and nitrogen in carbonaceous meteorites[END_REF] and oxygen [START_REF] Hashizume | Extreme oxygen isotope anomaly with a solar origin detected in meteoritic organics[END_REF]) reinforce this fact.

The most persuasive is the systematic enrichment in deuterium relative to terrestrial organic matter [START_REF] Remusat | Enrichment of deuterium in insoluble organic matter from primitive meteorites: A solar system origin?[END_REF][START_REF] Robert | The concentration and isotopic composition of hydrogen, carbon and nitrogen in carbonaceous meteorites[END_REF]. This deuterium enrichment is highly heterogeneous, as revealed by hydrogen isotopic studies at the molecular level [START_REF] Remusat | Enrichment of deuterium in insoluble organic matter from primitive meteorites: A solar system origin?[END_REF]) and at the nanoscale in NanoSIMS ion microprobe images [START_REF] Busemann | Interstellar Chemistry Recorded in Organic Matter from Primitive Meteorites[END_REF][START_REF] Remusat | Proto-Planetary Disk Chemistry Recorded by D-Rich Organic Radicals in Carbonaceous Chondrites[END_REF]. For instance, Orgueil meteorite contains small hot spots (micrometers in size) which are ranging in D/H ratio between 400-700x 10 -6 (Fig. 1.5) Fig. 1.5 NanoSIMS D/H images of Orgueil revealing the occurrence of small areas very enriched in D, called ''hot spots'' [START_REF] Remusat | The insoluble organic matter in carbonaceous chondrites: Chemical structure, isotopic composition and origin[END_REF] The same observation is reported for Murchison meteorite with D/H ratio 430x 10 - 6 [START_REF] Busemann | Interstellar Chemistry Recorded in Organic Matter from Primitive Meteorites[END_REF]). In addition, pulsed EPR was used to determine the isotopic composition of radicals in IOM of Orgueil [START_REF] Gourier | Extreme deuterium enrichment of organic radicals in the Orgueil meteorite: Revisiting the interstellar interpretation[END_REF]. It revealed that heterogeneously distributed radicals contain a very high deuterium concentration D/H= 15000±5000x10 -6 , much higher than the average bulk value D/H=350x10 -6 . This observation was confirmed by data from high spatial resolution ,quantitative isotopic NanoSIMS mapping by Remusat [START_REF] Remusat | Proto-Planetary Disk Chemistry Recorded by D-Rich Organic Radicals in Carbonaceous Chondrites[END_REF]. The heterogeneity of the deuterium enrichment is considered as the record of a complex history of the insoluble organic matter and it was proposed that deuterium exchange took place between pre-existing organic matter with low D/H ratios and D-rich gaseous molecules in the diffuse outer regions of the protoplanetary disk around the young Sun [START_REF] Remusat | Enrichment of deuterium in insoluble organic matter from primitive meteorites: A solar system origin?[END_REF].

Similar anomalies are present in nitrogen. Some carbonaceous chondrites for instance CR, CI and CM contain IOM enriched in 15 N compared to terrestrial organic matter. The δ 15 N of the standard Earth atmospheric N 2 is close to 0‰ whereas this value goes up to 400‰ in CR and CM chondrites. Recent use of the NanoSIMS ion probe provides information on the distribution of the nitrogen isotopic ratios and images of IOMs provide micron size areas with 15 N anomalies (Nakamura- [START_REF] Nakamura-Messenger | Organic Globules in the Tagish Lake Meteorite: Remnants of the Protosolar Disk[END_REF]. The analyzed hot spots are distributed all over the samples without a specific pattern.

Finally in case of oxygen and carbon the large fractionation is not observed in contrast to presolar grains [START_REF] Remusat | Organic and volatile elements in the solar system[END_REF]. It is believed that oxygen isotopes are controlled by the parent body alteration while the carbon isotopes correlate with the parent body temperature.

Formation of the solar system

It is widely accepted that the Solar System formed about 4.6 billion year ago, when gravity pulled together low-density cloud of interstellar gas and dust. Until now, number of theories have been established, beginning with the first model proposed by the French scientist René Descartes in 1663 [START_REF] Williams | A Survey of Theories Relating to the Origin of the Solar System[END_REF]. However many of these theories faced the obstacles and were more or less rejected.

Nowadays, there are five theories which are being considered:

 Solar Nebula Disk Model  Protoplanet Theory  Modern Laplacian Model  Capture Theory

 Accretion Theory

Nevertheless they do not explain all of the phenomena exhibited by the Solar System for instance: (1) the distribution of the angular momentum between Sun and planets, (2) a planet forming mechanism, (3) the division into terrestrial and giant planets, and (4) the formation of satellites [START_REF] Woolfson | The Solar -Origin and Evolution[END_REF].

Therefore, in the Solar Nebula Disk concept (Fig. 1.6) the Solar System formed from giant gaseous clouds which experienced gravitational collapse. The matter in the dense clouds of molecular hydrogen coalesces within itself to denser masses and rotating, form stars [START_REF] Pudritz | Clustered Star Formation and the Origin of Stellar Masses[END_REF]. This complex process of star formation supplemented with protoplanetary disk formation around young stars may give origin to planets under certain conditions, which are not yet fully understood. Hence the formation of planetary systems is assumed to be a natural effect of star formation.

The protoplanetary disk is an accretion disk that feeds the central star. Primarily very hot, the disk later cools down during the T tauri stage [START_REF] Andre | From T Tauri stars to protostars: Circumstellar material and young stellar objects in the rho Ophiuchi cloud[END_REF].

At this point, small dust grains are possibly produced which eventually may coalesce into planetesimals. If the disk is big enough, the runaway accretions begin, causing formation of Moon -to Mars -sized planetary embryos. Near the star, the planetary embryos go through a phase of violent mergers, creating terrestrial planets. The formation of giant planets is a little bit more complex process. It is thought to happen beyond the so-called frost line, where planetary embryos are mainly made of various types of ice. Consequently, the giant planets are more massive than those located in the inner part of the protoplanetary disk. Some embryos seem to continue to grow and eventually reach up to 10 Earth masses, the threshold value, which is necessary to begin accretion of the hydrogenhelium gas from the disk. The accretion ends when the gas is exhausted. Hence, ice giants such as Uranus and Neptune are thought to be failed cores, as they formed too late when the disk had almost disappeared [START_REF] Montmerle | Solar System Formation and Early Evolution: the First 100 Million Years[END_REF]. The Nebular hypothesis explains many of the basic features of the Solar System, but some features such as the problem of angular momentum are hardly accounted for by this hypothesis. As a result, other alternative theories must be considered as detailed below. In the Accretion Theory, which was suggested by the Soviet planetary scientist Otto Schmidt in 1944, the Sun is assumed to move through a dense interstellar cloud and to emerge surrounded by a dusty gaseous envelope. Schmidt believed, from energy considerations that, for two secluded bodies, the material from one could not be captured by the other and so he introduced another star (third body), to remove some energy. The need for a third body makes the model rather improbable because Lyttleton showed in 1961 that the cloud was of a large extent and the star-plus-cloud behaved like a many body system. Thus Lyttleton confirmed the capture of material by an accretion mechanism which was firstly suggested by Bondi and Hoyle in 1944 [START_REF] Woolfson | The origin and evolution of the solar system[END_REF].

In the Protoplanet Theory, suggested in 1960 [START_REF] Mccrea | Formation of the solar system -Brief review and revised protoplanet theory. The physics of the planets: Their origin[END_REF][START_REF] Mccrea | The Origin of the Solar System[END_REF] McCrea was trying to explain simultaneously the formation of the Sun and the planets and their slow rotation. The author presumed that starting materials like cloud of dust and gas are in a state of hypersonic turbulence. Thus, rapid internal collisions take place resulting in aggregation of masses at various places. Then, the use of different parameters like mass and radius of the cloud to explain the current state of the solar system, McCrea proposed a revised theory in 1988.

The Capture Theory, proposed by Woolfson in 1964, involves a tidal interaction between a condensed star (Sun) and a collapsing low density protostar. The Sun gravity would have drawn material from the diffuse atmosphere of the protostar, which would then have collapsed to form the planets [START_REF] Dormand | The Capture Theory and Planetary Condensation[END_REF]Woolfson 1971, Woolfson 1964).

The modern Laplacian Theory is derived from the Laplacian theory but it was extensively modelled by Prentice [START_REF] Prentice | Formation of the saturnian system: A modern Laplacian theory[END_REF]. He starts with a cool gas cloud, which condenses in a way that the angular momentum of the central body is only 1 percent of the system. Prentice assumes that the central condensate contains solid dust grains, which create drag in the gas. Eventually, after the core has slowed down, its temperature rises and the dust is evaporated. The slowly rotating core becomes the Sun. The planets form from the faster rotating cloud. His theory rather gives a mathematical explanation of the process of formation.

In recent years, the advanced astronomical observations at a variety of wavelengths, combined with developed numerical and theoretical models of the physical processes led to define possible ways how our solar system would have evolved through the various stages from gravitational collapse of a fragment of a molecular cloud to the accretion of planetary-sized bodies [START_REF] Collier | Rotational evolution of magnetic T Tauri stars with accretion discs[END_REF][START_REF] Alexander | The Early Evolution of the Inner Solar System: A Meteoritic Perspective[END_REF][START_REF] Shu | Star formation in molecular cloudsobservation and theory[END_REF][START_REF] Andre | From Prestellar Cores to Protostars: the Initial Conditions of Star Formation[END_REF]. Yet, the details of the formation steps remain unclear. Fortunately, the chondritic meteorites as undifferentiated bodies are one of the facts which can deliver convincing explanation and help in reconstructing the chronology of the formation of the Solar System. The events during the early evolution are "remembered" by the components of chondrites and recorded in the chemical, and especially, isotopic compositions of the host mineral assemblages; thus the characterization and their formation processes are fundamental to the science of the Solar System early history.

Organics in space

Compounds containing carbon-hydrogen bonds of covalent character are defined as organic compounds. It is well known that these molecules are ubiquitous throughout the Galaxy and even the universe [START_REF] Kwok | Enrichment of the solar system by organic compounds delivered from evolved stars[END_REF]. Nevertheless, to understand where they come from and if they could form the basis for the origin of life it is necessary to know their lifecycle from their formation in the outflows of evolved stars to the interstellar medium and consequently through the star-forming clouds to protoplanetary disk. As different molecules are found in various environments, ranging from nearby objects in our solar system to distant sources in the "early universe", the following chapter will discuss the diversity of the organics in interstellar matter and protoplanetary disk.

Interstellar Matter

The interstellar medium (ISM) contains different environments where large difference in the temperature 10-10 4 K occurs along with great variation in densities 1-10 8 H atoms cm -3 . It comprises gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. Here the organic molecules take part in the formation of new stars and the evolved stars return the products of nucleosynthesis. The interstellar matter contains primarily hydrogen and helium with traces amounts of carbon, oxygen and nitrogen. The next paragraph will consider two different components of ISM dense molecular clouds and diffuse clouds.

Dense molecular clouds in the ISM

The dense interstellar clouds are often called molecular clouds as their composition is primarily molecular. The gas in these regions is predominantly H 2 .

Nevertheless observations at infrared, radio, millimetre and submillimetre frequencies show large variety of gas phase organic molecules [START_REF] Irvine | Chemical Abundances in Molecular Clouds[END_REF][START_REF] Ohishi | Chemical and physical evolution of dark clouds Molecular spectral line survey toward TMC-1[END_REF][START_REF] Winnewisser | Spectroscopy Between the Stars[END_REF] with densities between 100 cm -3 to 10 8 cm -3 . Here we can include nitriles, aldehydes, alcohols, acids ethers, ketones, amines, amides along with long (n<10) chain hydrocarbon compounds. As dense interstellar clouds structure is quite complex, three different areas with organic molecules can be distinguished: grain surfaces, cold dark clouds and hot molecular cores where the organic compounds are formed and observed. These regions will be separately described in the following.

Grain surface. The dust particles occurring in cold molecular clouds are an important "catalyst" which is involved in long reactions of atoms or molecules from the gas (Charnley, Tielens and[START_REF] Charnley | Deuterated Methanol in the Orion Compact Ridge[END_REF]Charnley 1997). There are three major mechanisms for surface reactions: the diffuse (Langmuir-Hinshelwood) or the Eley-Rideal (mechanism proposed in 1938 by D. D. Eley andE. K. Rideal (Eley 1948)) or the hot atom interaction (Fig. 1.7). Nevertheless, astrochemical models often include only the diffusive one as it is the best studied [START_REF] Kolasinski | Surface Science: Foundations of Catalysis and Nanoscience[END_REF]. [START_REF] Tielens | Model calculations of the molecular composition of interstellar grain mantles[END_REF].

Similar syntheses occur in case of NH 3 and CH 4 . Similarly, an active chemistry on the surface of grains leads to complex species such as CH 3 OH, CO, CO 2 , CH 4 , OCS, HCOOH, H 2 CO OCN - [START_REF] Dartois | The second most abundant ice species towards the high-mass protostars RAFGL7009S and W 33A[END_REF][START_REF] Gerakines | Observations of Solid Carbon Dioxide in Molecular Clouds with the Infrared Space Observatory[END_REF] along with more complex organics like PAHs [START_REF] Whittet | An ISO SWS view of interstellar ices: first results[END_REF][START_REF] D'hendecourt | ISO-SWS observations of solid state features towards RAFGL 7009[END_REF][START_REF] Schutte | Further evidence for the OCN-assignment to the XCN band in astrophysical ice analogs[END_REF][START_REF] Ehrenfreund | Infrared spectroscopy of interstellar apolar ice analogs[END_REF][START_REF] Gibb | An Inventory of Interstellar Ices toward the Embedded Protostar W33A[END_REF]. Nevertheless, it has to be considered that other reaction processes take place on or in the ice mantles. As dust grains are transported from cold sections to warm protostellar regions, additional parameters (temperature, UV irradiation, cosmic rays bombardment) may have influenced the grain mantle conditions. Table 1.1 consists the most recent abundances of interstellar ices near high-mass, low-mass and field stars. Table 1.1 Most abundant species observed in different regions of dense clouds and in the comae of bright comets, their abundances relative to H 2 0 [START_REF] Ehrenfreund | Organic Molecules in the Interstellar Medium, Comets, and Meteorites: A Voyage from Dark Clouds to the Early Earth[END_REF] Different groups of organic compounds are identified in cold dark clouds region.

As the cosmic rays penetrate throughout, they initiate a rich ion-molecule chemistry accompanied by neutral-neutral reactions forming number of complex organic molecules [START_REF] Herbst | A detailed investigation of proposed gas-phase syntheses of ammonia in dense interstellar clouds[END_REF][START_REF] Prasad | Chemical Evolution of Molecular Clouds[END_REF][START_REF] Millar | The UMIST database for astrochemistry[END_REF][START_REF] Herbst | Gas-phase production of complex hydrocarbons, cyanopolyynes, and related compounds in dense interstellar clouds[END_REF]. These processes, along with grain surface chemistry, explain the high observed D/H ratios in interstellar molecules [START_REF] Tielens | Surface chemistry of deuterated molecules[END_REF][START_REF] Millar | Deuterium fractionation in dense interstellar clouds[END_REF]). In the cold dark clouds, there are identified unsaturated carbon chain molecules [START_REF] Ohishi | Chemical and physical evolution of dark clouds Molecular spectral line survey toward TMC-1[END_REF] like cyanopolyynes, chain radicals, methylated molecules such as methylcyanoacetylene (CH 3 CCCN) and methyldiacetylene (CH 3 CCCCH). Furthermore several small molecules (CCO, CCCO, CCS, CCCS) are detected, their higher homologues [START_REF] Langer | First Astronomical Detection of the Cumulene Carbon Chain Molecule H2C6 in TMC-1[END_REF], McCarthy et al. 1997[START_REF] Guelin | Detection of a new linear carbon chain radical: C 7[END_REF][START_REF] Guelin | Astronomical detection of the cyanobutadiynyl radical C 5 N[END_REF][START_REF] Thaddeus | New carbon chains in the laboratory and in interstellar space[END_REF][START_REF] Bell | Observations of Long CnH Molecules in the Dust Cloud TMC-1[END_REF].

Numerous attempts at modelling the cold core TMC-1 chemistry were performed based on the ion-molecule pathway [START_REF] Huntress | The synthesis of complex molecules in interstellar clouds[END_REF][START_REF] Leung | Synthesis of complex molecules in dense interstellar clouds via gas-phase chemistry -A pseudo time-dependent calculation[END_REF][START_REF] Millar | Chemical modelling of molecular sources -I. TMC-1[END_REF][START_REF] Millar | How abundant are complex interstellar molecules?[END_REF][START_REF] Millar | Chemical modelling of molecular sources -IV. Time-dependent chemistry of dark clouds[END_REF][START_REF] Herbst | The gas phase production of CH2CN and other organo-nitrogen species in dense interstellar clouds[END_REF]) . Subsequently, it was realized that neutralneutral reactions play an important role in the production of observed carbon chain molecules [START_REF] Cherchneff | The formation of cyanopolyyne molecules in IRC + 10216[END_REF] Hot molecular cores, which are enriched in deuterium, are mostly rich in complex organic molecules but also in water and ammonia [START_REF] Tielens | Circumstellar and Interstellar Synthesis of Organic Molecules[END_REF][START_REF] Blake | Molecular abundances in OMC-1 -The chemical composition of interstellar molecular clouds and the influence of massive star formation[END_REF][START_REF] Van Dishoeck | The chemical evolution of protostellar and protoplanetary matter[END_REF][START_REF] Sutton | The distribution of molecules in the core of OMC-1[END_REF][START_REF] Irvine | Comets: A link between interstellar and nebular chemistry[END_REF].

Molecules identified in hot cores can have three (cold, warm-up and hot-core phases) possible origins as described below.

First, cold phase considers atom accumulation on the cold grain surfaces followed by molecules formed in the gas phase such as CO, HCN, acetylene [START_REF] Lahuis | ISO-SWS spectroscopy of gas-phase C 2 H 2 and HCN toward massive young stellar objects[END_REF] and unsaturated carbon chains. Surface chemistry forms simple ices CO 2 and water, like also complex saturated species. where 2H is shown, a barrier penetration reaction followed by an exothermic addition is implicitly indicated. Molecules in blue are detected in star-forming regions. Provided by S. Charnley [START_REF] Charnley | The bridge between the big bang and biology : stars, planetary systems, atmospheres, volcanoes : their link to life[END_REF] Second, the warm up phase occurs when the material flows inward toward the protostar warms from 10K to 100K-300K. During this process, the sublimation of the mixed ice mantles on the dust grain happens. As this organic formation route does not occur in a simple manner, gas phase chemistry was considered by Viti and Williams [START_REF] Viti | Time-dependent evaporation of icy mantles in hot cores[END_REF] as well as gaseous and surface chemistries by [START_REF] Garrod | Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores[END_REF]) and radicalradical reactions by Hollis & Churchwell [START_REF] Hollis | Functional Molecular Groups on Interstellar Grains[END_REF] and [START_REF] Allen | The molecular composition of dense interstellar clouds[END_REF]. Here the grain surface reactions produce simple saturated molecules like water and ammonia [START_REF] Brown | A model of the chemistry in hot molecular cores[END_REF].

Finally, the last third region is the hot core phase one where only gas phase chemistry takes place as the temperature goes higher than 300 K. Evaporation of simple, compositional different molecular (complex O-bearing and N-bearing molecules) mantles drives the gas phase complexity [START_REF] Charnley | On the molecular complexity of the hot cores in Orion A -Grain surface chemistry as 'The last refuge of the scoundrel[END_REF]. In this region, many more reactions occur, including endothermic and exothermic processes. Here many models were established and for instance by Blake [START_REF] Blake | Molecular abundances in OMC-1 -The chemical composition of interstellar molecular clouds and the influence of massive star formation[END_REF]) who presented a chemical model which explains the presence of oxygen-containing complex molecules. By radiative association of CH + and H 2 O, the protonated methanol can act as precursor in ion molecule reaction leading to species like dimethyl ether or methyl formate [START_REF] Millar | The formation of oxygen-containing organic molecules in the Orion compact ridge[END_REF].

Diffuse ISM

In the diffuse clouds, which are characterized by an average temperature of ~100K and densities 100-300 cm -1 , most molecules are photodissociated by interstellar UV photons (≈10 8 photons cm -2 s -1 ) [START_REF] Mathis | Interstellar radiation field and dust temperatures in the diffuse interstellar matter and in giant molecular clouds[END_REF].

Thus diffuse and translucent molecular clouds are rich in the simplest organics CH, CH + , C 3 H 2 , CN, HCOC, CO, OH, C 2 , HCN, HNC, CN, CS and H 2 CO [START_REF] Lucas | Molecules in Astrophysics[END_REF] along with recently detected C 2 H and C 3 H 2 [START_REF] Liszt | The structure and stability of interstellar molecular absorption line profiles at radio frequencies[END_REF]. However, much more complex organic materials do exist in this environment, which can efficiently distribute the energy of absorbed photons through many vibrational modes [START_REF] Tielens | Circumstellar and Interstellar Synthesis of Organic Molecules[END_REF]. Among them, an important feature are the so-called diffuse interstellar bands (DIBs) which are tentatively proposed to be due to polycyclic aromatic hydrocarbons and other large carbon-bearing molecules. To date, the origin of DIBs is still debated and their individual molecular carriers have not yet been identified, although laboratory measurements assigned the two bands at 9,632 and 9,577 Å to C 60 + molecules which is responsible for only two DIB's [START_REF] Campbell | Laboratory confirmation of C60+ as the carrier of two diffuse interstellar bands[END_REF].

About 1% per mass of the interstellar medium is locked in solid dust grains, which may be composed of silicates, amorphous carbon, hydrogenated amorphous carbon, diamonds, organic refractories, and carbonaceous networks such as soot, graphite, quenched-carbonaceous condensates (Fig. 1.9). Moreover proposed by Desert [START_REF] Desert | Interstellar dust models for extinction and emission[END_REF])) a three-component model suggests that interstellar dust consists the coexistence of big grains (silicates with refractory mantles), very small grains (VSG, carbonaceous) and polycyclic aromatic hydrocarbons (PAHs).

It is admitted that the organic material present in the diffuse interstellar medium can originate through one of the following three pathways: i) by gas phase reactions where model calculations of dispersing clouds allow the formation of molecules up to 64 C atoms with ion-molecule reactions and neutralneutral reactions [START_REF] Bettens | The Abundance of Very Large Hydrocarbons and Carbon Clusters in the Diffuse Interstellar Medium[END_REF][START_REF] Herbst | Chemistry in the Interstellar Medium[END_REF][START_REF] Ruffle | The Abundance of C7in Diffuse Clouds[END_REF] ii)by reactions in circumstellar envelopes and subsequent mixing into the diffuse medium [START_REF] Tielens | Surface chemistry of deuterated molecules[END_REF]Charnley 1997, Frenklach and[START_REF] Frenklach | Formation of polycyclic aromatic hydrocarbons in circumstellar envelopes[END_REF] iii)from carbonaceous dust by photochemical reactions and grain collisions. Grain surface reactions have also been suggested but only simple hybrides like NH are expected to be formed [START_REF] Wagenblast | On the origin of NH in diffuse interstellar clouds[END_REF]. The outer Solar System, for instance on the surface of asteroids belt, in the atmosphere of Saturn's moon Titan, possibly on the moon Triton and certainly in comets [START_REF] Cruikshank | Organic Matter in the Outer Solar System: From the Meteorites to the Kuiper Belt[END_REF]), seems to be more abundant in carbonaceous matter than previously discussed regions of cold clouds, hot cores and diffuse clouds.

Comets

Great amount of volatile organics is observed in comets [START_REF] Bockelée-Morvan | New molecules found in comet C/1995 O1 (Hale-Bopp). Investigating the link between cometary and interstellar material[END_REF][START_REF] Biver | Radio wavelength molecular observations of comets C/1999 T1 (McNaught-Hartley), C/2001 A2 (LINEAR), C/2000 WM1 (LINEAR) and 153[END_REF]) which clearly contain the highest portion of volatiles with respect to other small solar system bodies. It is admitted that the nuclei of comets are composed of ice, rock, and large organic entities (CHON particles -carbon, hydrogen, oxygen, and nitrogen [START_REF] Mumma | Soft X-Rays From Four Comets Observed With EUVE[END_REF]Abbott 1997, Irvine et al. 2000). Their chemical composition has been constrained by Greenberg [START_REF] Greenberg | Making a comet nucleus[END_REF] [START_REF] Crovisier | Remote Observations of the Composition of Cometary Volatiles[END_REF][START_REF] Mumma | Comets and the origin of the solar system -Reading the Rosetta Stone[END_REF][START_REF] Rodgers | HNC and HCN in Comets[END_REF]). Most of these compounds are parent species evaporating directly from the ices. The origin of comets is still quite far from being fully understood. Three models are considered: the interstellar model, which suggests that interstellar grains agglomerated to form cometary nuclei in the cold outer solar nebula far from the protosun [START_REF] Wilkening | Comets[END_REF]; the complete chemical equilibrium model, in which presolar material is altered and chemically equilibrated [START_REF] Lunine | Sublimation and reformation of Icy grains in the primitive solar nebula[END_REF]; and an intermediate model in which presolar material has been chemically and physically processed [START_REF] Chick | Thermal Processing of Interstellar Dust Grains in the Primitive Solar Environment[END_REF]Cassen 1997, Fegley 1999). At present it is presumed that comets are a mixture of interstellar and nebular material [START_REF] Mumma | Comets and the origin of the solar system -Reading the Rosetta Stone[END_REF][START_REF] Irvine | The Composition of Interstellar Molecular Clouds[END_REF]) and their composition may vary according to their place of origin. Finally, it has to be noted, that after the Stardust mission many complex organics have been found with heterogeneous distribution in abundance and composition among particles [START_REF] Matrajt | Carbon investigation of two Stardust particles: A TEM, NanoSIMS, and XANES study[END_REF]. Here there are organic species like PAHs (with few ring aromatic ringsgenerally smaller then PAHs detected in diffuse clouds) [START_REF] Sandford | Organics Captured from Comet 81P/Wild 2 by the Stardust Spacecraft[END_REF] and a new class of aromatic-poor compounds comparable with these in meteorites and interplanetary dust particles (IDPs).

Carbonaceous chondrites

The most chemically complex and well characterized organic matter has been found in carbonaceous chondrites. These most primitive and least processed meteorites contain organics which hold key information about the chemical composition of the gas that formed our Sun and the planets.

Carbonaceous chondrites comprise up to 4% of carbon, mostly in the form of organic matter, with minor fractions of carbonates, elemental carbon phases (graphite and nanodiamonds) and refractory carbides. The organic matter occurs throughout the matrix along with clay minerals and oxides. It is composed mostly of carbon with hydrogen, oxygen, nitrogen or sulfur. It can be divided into two fractions:

the soluble and insoluble components Less abundant, accounting for up to 30% of meteoritic organic matter in CI1 (Orgueil) and CM2 (Murchison) meteorites [START_REF] Sephton | Organic compounds in carbonaceous meteorites[END_REF], the soluble matter (SOM) can be isolated from meteorites by extraction in common organic solvents. Thanks to many available analytical techniques, SOM has been extensively analyzed for the last 50 years and a large variety of soluble organic compounds was revealed [START_REF] Botta | Extraterrestrial Organic Compounds in Meteorites[END_REF][START_REF] Sephton | Recognizing life in the Solar System: guidance from meteoritic organic matter[END_REF][START_REF] Hayes | Organic constituents of meteorites-a review[END_REF][START_REF] Hayatsu | Organic compounds in meteorites and their origins[END_REF][START_REF] Mullie | Organic-matter in carbonaceous chondrites[END_REF][START_REF] Cronin | Organic Matter in Meteorites: Molecular and Isotopic Analyses of the Murchison Meteorite[END_REF] (Fig. 1.10). In Murchison the most abundant soluble compounds are carboxylic acids [START_REF] Yuen | Monocarboxylic Acids in Murray and Murchison Carbonaceous Meteorites[END_REF][START_REF] Yuen | Carbon isotope composition of low molecular weight hydrocarbons and monocarboxylic acids from Murchison meteorite[END_REF][START_REF] Krishnamurthy | Isotopic and molecular analyses of hydrocarbons and monocarboxylic acids of the Murchison meteorite[END_REF]) amino acids [START_REF] Kvenvolden | Evidence for Extraterrestrial Amino-acids and Hydrocarbons in the Murchison Meteorite[END_REF] sugar derivatives [START_REF] Cooper | Carbonaceous meteorites as a source of sugar-related organic compounds for the early Earth[END_REF]) and nucleobases [START_REF] Martins | Extraterrestrial nucleobases in the Murchison meteorite[END_REF]. Other oxidized compounds have been detected: alcohols, aldehydes and ketones. Aromatic and aliphatic hydrocarbons also occur in The remaining 70% of organic matter is present as high molecular weight macromolecular material and is insoluble in common solvents [START_REF] Hayes | Organic constituents of meteorites-a review[END_REF]. Carbon (Murchison -50 wt%, Orgueil -67wt%, [START_REF] Derenne | Use of Combined Spectroscopic and Microscopic Tools for Deciphering the Chemical Structure and Origin of the Insoluble Organic Matter in the Orgueil and Murchison Meteorites[END_REF]), hydrogen (Murchison -2.92 wt%, Orgueil -4.07wt% [START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF]) and oxygen (Orgueil -16.5% wt%, Murchison -14.5% wt%, [START_REF] Derenne | Model of molecular structure of the insoluble organic matter isolated from Murchison meteorite[END_REF]) are the main elements of insoluble organic matter (IOM) with nitrogen (2.7-2.8 wt% and 1.05-2 wt% for Orgueil and Murchison, respectively, (Remusat et al. 2005b[START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF]) and sulfur (4 wt% for Orgueil, 12.5 wt% for Murchison, (Remusat et al. 2005b)).as a minor heteroatoms. IOM is isolated from the bulk rock through successive water and solvent extractions as well as hydrolyses to remove soluble and hydrolysable organic compounds and further acid (HF/HCl) treatments to dissolve most of the mineral matrix [START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF]. However, the acid residue is not pure organic matter and it still contains non dissolved oxides, sulfides and nanodiamonds [START_REF] Lewis | Host phase of a strange xenon component in Allende[END_REF]. It has to be mentioned that this treatment which is commonly used to isolate kerogen from sedimentary rocks is considered not to alter the IOM [START_REF] Durand | Procedures for kerogen isolations[END_REF] For long, IOM was less studied than SOM due to its high molecular weight and associated analytical difficulties. Nevertheless, the molecular structure of IOM from the carbonaceous chondrites Murchison and Orgueil has been investigated during the last few decades using a large set of both destructive and non-destructive analytical techniques. The latter include elemental analysis [START_REF] Alexander | The origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter[END_REF]), thermal and chemical degradations followed by gas chromatography ⁄ mass spectrometry (py-GCMS [START_REF] Studier | Origin of organic matter in early solar system-V. Further studies of meteoritic hydrocarbons and a discussion of their origin[END_REF][START_REF] Levy | The organic analysis of the murchison meteorite[END_REF][START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF][START_REF] Hayatsu | Comparative Structural Study of Meteoritic Polymer with Terrestrial Geopolymers Coal and Kerogen[END_REF][START_REF] Hayatsu | Phenolic Ethers in the Organic Polymer of the Murchison Meteorite[END_REF][START_REF] Komiya | Organic compounds from insoluble organic matter isolated from the Murchison carbonaceous chondrite by heating experiments[END_REF], Sephton et al. 2000[START_REF] Sephton | Aromatic units from the macromolecular material in meteorites: Molecular probes of cosmic environments[END_REF][START_REF] Sephton | Organic matter in ancient meteorites[END_REF][START_REF] Remusat | Enrichment of deuterium in insoluble organic matter from primitive meteorites: A solar system origin?[END_REF], Remusat, Derenne and Robert 2005a, Remusat et al. 2005b[START_REF] De Vries | A search for C60 in carbonaceous chondrites[END_REF][START_REF] Huang | Structure and isotopic ratios of aliphatic side chains in the insoluble organic matter of the Murchison carbonaceous chondrite[END_REF], Yabuta et al. 2007), number of different spectroscopies such as Fourier transform infrared spectroscopy (FTIR), solid state nuclear magnetic resonance (NMR), X-ray absorption near-edge spectroscopy (XANES) [START_REF] Cody | NMR studies of chemical structural variation of insoluble organic matter from different carbonaceous chondrite groups[END_REF][START_REF] De Gregorio | Isotopic and chemical variation of organic nanoglobules in primitive meteorites[END_REF][START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF][START_REF] Guillou | Evolution of organic matter in Orgueil, Murchison and Renazzo during parent body aqueous alteration: In situ investigations[END_REF][START_REF] Orthous-Daunay | Speciation of sulfur in the insoluble organic matter from carbonaceous chondrites by XANES spectroscopy[END_REF][START_REF] Danger | Characterization of laboratory analogs of interstellar/cometary organic residues using very high resolution mass spectrometry[END_REF]) Raman spectroscopy [START_REF] Bonal | Determination of the petrologic type of CV3 chondrites by Raman spectroscopy of included organic matter[END_REF][START_REF] Bonal | Organic matter and metamorphic history of CO chondrites[END_REF][START_REF] Busemann | Characterization of insoluble organic matter in primitive meteorites by microRaman spectroscopy[END_REF][START_REF] Quirico | Metamorphic grade of organic matter in six unequilibrated ordinary chondrites[END_REF][START_REF] Quirico | Origin of insoluble organic matter in type 1 and 2 chondrites: New clues, new questions[END_REF], electron paramagnetic resonance [START_REF] Binet | Occurence of abundant diradicaloid moieties in the insoluble organic matter from the Orgueil and Murchison meteorites: a fingerprint of its extraterrestrial origin?[END_REF], Binet et al. 2002) and high resolution transmission electron microscopy, [START_REF] Derenne | Size discontinuity between interstellar and chondritic aromatic structures: A high-resolution transmission electron microscopy study[END_REF][START_REF] Guillou | High resolution TEM of chondritic carbonaceous matter: Metamorphic evolution and heterogeneity[END_REF]. The elemental analysis of IOM isolated from Murchison reveals that the macromolecular structure is rather aromatic with H/C ratio about 0.7 [START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF][START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF][START_REF] Komiya | Organic compounds from insoluble organic matter isolated from the Murchison carbonaceous chondrite by heating experiments[END_REF][START_REF] Robert | The concentration and isotopic composition of hydrogen, carbon and nitrogen in carbonaceous meteorites[END_REF][START_REF] Hayatsu | Organic compounds in meteorites and their origins[END_REF][START_REF] Yabuta | Solid-state 13C NMR characterization of insoluble organic matter from Antarctic CM2 chondrites: Evaluation of the meteoritic alteration level[END_REF]). This statement is further supported by solid state 13 C NMR which shows that most carbon atoms (50-80%) are present in aromatic structures whereas the rest is in aliphatic bonds and that these aromatic carbons are protonated [START_REF] Cronin | 13C NMR spectroscopy of the insoluble carbon of carbonaceous chondrites[END_REF][START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF], Cody and Alexander 2005) (Fig. 1.11).

Fig. 1.11 Solid-state 13 CNMR spectrum of Orgueil IOM, from [START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF].

The chemical shift (in ppm) is characteristic of the functional group. This picture demonstrates the strong aromatic behavior of the IOM. Moreover, the deconvolution of the signal allows the determination of the contribution of each type of C atom, leading to their distribution in the molecular structure.

Two hypotheses could then be put forward to account for this aromaticity: either aromatic units are very large or if smaller, they must be highly substituted [START_REF] Derenne | Model of molecular structure of the insoluble organic matter isolated from Murchison meteorite[END_REF]. Moreover the aromatic nature of the IOM is evidenced by pyrolysis coupled with GC-MS (Remusat et al. 2005b[START_REF] Komiya | Organic compounds from insoluble organic matter isolated from the Murchison carbonaceous chondrite by heating experiments[END_REF], Sephton et al. 2000) and oxidative degradation (Remusat et al. 2005a). The presence of polyaromatics (indene, acenapthene) and high degree of carboxylation of the aromatic oxidation products also pointed to an aromatic structure of IOM (Remusat et al. 2005a). However, these techniques did not provide any information on the size of the aromatic units and HRTEM was used to provide direct images of polyaromatic layers ( Fig. 1.12) The aromatic layers appear as fringes which are rather small (0.25 and 1 nm in diameter) corresponding to two to three rings [START_REF] Derenne | Size discontinuity between interstellar and chondritic aromatic structures: A high-resolution transmission electron microscopy study[END_REF].

Fig. 1.12 HRTEM observation of the insoluble organic matter isolated from the Murchison meteorite: raw image and skeletonized image (left). A similar picture has been observed for the Orgueil meteorite. The side of the picture corresponds to 9.7 nm. Average structural parameters of the aromatic units in Orgueil and Murchison (right) [START_REF] Derenne | Size discontinuity between interstellar and chondritic aromatic structures: A high-resolution transmission electron microscopy study[END_REF] Finally, EPR analysis and theoretical calculation led to propose that aromatic moieties comprise 3-4 rings in diameter confirming the aforementioned previous estimations from HRTEM [START_REF] Gourier | Search for EPR markers of the history and origin of the insoluble organic matter in extraterrestrial and terrestrial rocks[END_REF]).

Fourier transform infrared and 13 C NMR show that aliphatic carbons contribute to the macromolecular structure of IOM. The CH 2 to CH 3 ratios obtained from both techniques reveal the high branching level in the aliphatic chains (Gardinier et al. 2000, Ehrenfreund, Robert and[START_REF] Ehrenfreund | Similarity of the infrared spectrum of an Orgueil organic polymer with interstellar organic compounds in the line of sight towards IRS 7[END_REF]. The presence of aliphatic linkages was also inferred by chemical degradation such as sodium dichromate oxidation [START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF] or ruthenium tetroxide oxidation (Fig. 1.13; (Remusat et al. 2005a)). These studies revealed that the aromatic moieties were linked by aliphatic chains comprising from 2-9 carbon atoms. Moreover these aliphatic chains were shown to exhibit a high degree of cross-linking [START_REF] Hayatsu | Phenolic Ethers in the Organic Polymer of the Murchison Meteorite[END_REF][START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF][START_REF] Cody | Solid-state (1H and 13C) nuclear magnetic resonance spectroscopy of insoluble organic residue in the Murchison meteorite: a self-consistent quantitative analysis[END_REF][START_REF] Sephton | Organic matter in ancient meteorites[END_REF], Remusat et al. 2005a, Remusat et al. 2005b), definitely different from terrestrial organic compounds such as kerogen.

Fig. 1.13 TIC of RuO 4 oxidation products of the IOM. The acids are detected as their trimethylsilyl esters (Remusat et al. 2005a) Finally, in addition to atoms of carbon and hydrogen the IOM is built of heteroelements like oxygen, nitrogen and sulfur. The presence of these elements was confirmed by elemental analysis, 13 C solid state NMR, XANES and pyrolysis. For instance, oxygen, the most abundant heteroatom in the IOM, was localized by C-XANES [START_REF] Wirick | Organics in the Murchison meteorite using carbon XANES spectroscopy[END_REF]) and solid state 13 C NMR [START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF][START_REF] Cody | Solid-state (1H and 13C) nuclear magnetic resonance spectroscopy of insoluble organic residue in the Murchison meteorite: a self-consistent quantitative analysis[END_REF] pointing to various aromatic ketones and phenols, carboxyl and carbonyl groups. When pyrolysis is concerned, rather low abundance of oxygenated compounds was observed as polar compounds are often not GC-amenable (Remusat et al. 2005b[START_REF] Sephton | Small-scale hydrous pyrolysis of macromolecular material in meteorites[END_REF][START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF]. To overcome this problem, pyrolysis was performed in the presence of tetramethylammonium hydroxide (TMAH) which acts as both a base and a methylation agent. As a result, the cleavage of the polar bonds is enhanced and the pyrolysis products are methylated in situ. The presence of ether and ester groups in the aliphatic linkages between aromatic moieties was thus revealed (Remusat et al. 2005a).

Number of sulfur products containing thiophene rings were detected by pyrolysis [START_REF] Levy | The organic analysis of the murchison meteorite[END_REF][START_REF] Komiya | Organic compounds from insoluble organic matter isolated from the Murchison carbonaceous chondrite by heating experiments[END_REF], Remusat et al. 2005b). However, aromatization upon pyrolysis is known to yield thiophenes and the relative amount of aliphatic sulfides to thiophenes was assessed through XANES [START_REF] Derenne | Use of Combined Spectroscopic and Microscopic Tools for Deciphering the Chemical Structure and Origin of the Insoluble Organic Matter in the Orgueil and Murchison Meteorites[END_REF][START_REF] Orthous-Daunay | Speciation of sulfur in the insoluble organic matter from carbonaceous chondrites by XANES spectroscopy[END_REF]). Finally, one nitrogen containing compound (benzonitrile) is commonly identified in IOM pyrolysates and nitriles and pyrroles were revealed via 15 N NMR (Remusat et al. 2005b). It has to be noted that the following model (Fig. 1.15) accounts for molecular units (atoms or functional groups) whose abundance is higher than 3%. As aromatic moieties are highly substituted and aliphatic chains highly branched, it was reasonably assumed that the IOM chemical structure resulted from cyclisation and aromatization of small aliphatic units derived from CH 3 , CH 2 and CH radicals (Fig. 1.17) which were present in space in the gas phase. Moreover, they consider that possible synthesis of IOM isolated from carbonaceous chondrites might take place in warm regions (up to 650K) of the ProtoSolar Nebula as it had been discovered that deuterium enrichment could be a secondary process [START_REF] Remusat | Enrichment of deuterium in insoluble organic matter from primitive meteorites: A solar system origin?[END_REF].

Murchison and the

Fig. 1.17 Illustration of a possible formation pathway of aromatic moieties in the gas phase. The starting drawing accounts for an ion or radical with four carbon atoms. The scheme does not take into account heteroelements (Derenne and Robert 2010)

Laboratory synthesis of organic matter

The list of organic molecules in space is extensive and sometimes to recognize new species, long lasting observations are needed. The most basic required information is spectroscopy of materials from UV to millimeter wavelengths.

Moreover, the obtained data has to be followed up by sometimes most difficult interpretation of observations of astronomical sources. Nevertheless to make the next step in understanding organics the need for laboratory synthesis is compulsory. To obtain rates for various reactions that are expected to form and destroy organics under space conditions is crucial and, along with observational evidence, it will help establishing the cycle of organic molecules in different environments in the Galaxy.

Several attempts to synthesize analogues of extraterrestrial organic matter have been reported so far. They often aim at reconciling the spectroscopic observations on astrophysical media with those obtained on synthetic organic matter. Various targets are distinguished in the literature such as cometary ices, interstellar organic molecules (on grains or in the gas phase gas), interplanetary dust particles (IDPs), meteorites, or Titan's aerosols. As a result, different experimental devices have been set up.

Tholins

Saturn's moon atmosphere consists of about 98% nitrogen and 2% methane along with minor amounts of other species including H 2 , HCN, CO and organics such as ethane, ethylene, acetylene and cyanoacetylene [START_REF] Niemann | The abundances of constituents of Titan's atmosphere from the GCMS instrument on the Huygens probe[END_REF].

Consequently, Titan tholins are a class of heteropolymer molecules formed by solar ultraviolet irradiation and also by energetic particle bombardment of the major gaseous atmospheric compounds: N 2 and CH 4 . Monomeric, oligomeric and polymeric products are produced and tholins contain an extraordinary amount of compounds differing in molecular weight and in the nature of atoms and functions. Some observational data provides information about the distribution, size and optical properties of these aerosols [START_REF] Tomasko | Photometry and polarimetry of Titan: Pioneer 11 observations and their implications for aerosol properties[END_REF][START_REF] Rages | Size estimates of Titan's aerosols based on Voyager high-phase-angle images[END_REF][START_REF] West | Evidence for aggregate particles in the atmospheres of Titan and Jupiter[END_REF][START_REF] West | Voyager 2 photopolarimeter observations of Titan[END_REF]). Nevertheless, this information is not sufficient to determine the physico-chemical properties and to answer the question how they were formed. Therefore numerous laboratory experiments have been developed to produce analogues of Titan's aerosols. It is acknowledged that photon is the main source of energy deposition in Titan's atmosphere and for this reason different light sources have been used. For instance Xenon arcs [START_REF] Podolak | Photochemical aerosols in Titan's atmosphere[END_REF], mercury or hydrogen lamps (Bar-Nun, [START_REF] Bar-Nun | Shape and optical properties of aerosols formed by photolysis of acetylene, ethylene, and hydrogen cyanide[END_REF][START_REF] Dodonova | Activation of nitrogen by vacuum UV irradiation[END_REF][START_REF] Scattergood | Titan's aerosols I. Laboratory investigations of shapes, size distributions, and aggregation of particles produced by UV photolysis of model Titan atmospheres[END_REF] are the reaction sources but as the UV photons are not transmitted through the silica windows of the UV light sources the photodissociation of N 2 is reduced. The mixture of methane with nitrogen has therefore been replaced with nitrogen-containing compounds (HCN and HC 3 N) in other attempts [START_REF] Podolak | Photochemical aerosols in Titan's atmosphere[END_REF][START_REF] Clarke | Titan Haze: Structure and Properties of Cyanoacetylene and Cyanoacetylene-Acetylene Photopolymers[END_REF][START_REF] Clarke | The Design and Use of a Photochemical Flow Reactor: A Laboratory Study of the Atmospheric Chemistry of Cyanoacetylene on Titan[END_REF][START_REF] Tran | Simulation of Titan haze formation using a photochemical flow reactor: The optical constants of the polymer[END_REF]. Moreover different types of plasmas were used in the gas phase to carry out production tholins, for example: radio-frequency inductive coupled plasma discharge [START_REF] Khare | Optical constants of organic tholins produced in a simulated Titanian atmosphere: From soft x-ray to microwave frequencies[END_REF][START_REF] Imanaka | Laboratory experiments of Titan tholin formed in cold plasma at various pressures: implications for nitrogencontaining polycyclic aromatic compounds in Titan haze[END_REF]), direct current discharge [START_REF] Coll | Experimental laboratory simulation of Titan's atmosphere: aerosols and gas phase[END_REF] or corona discharges [START_REF] Ramirez | Experimental Simulation of Titan's Atmosphere by Cold Plasmas[END_REF]. It has to be noted that, in contrast to previous syntheses, in the PAMPRE device (dusty plasma experiment) Titan's atmosphere is mimicked using levitation conditions avoiding product deposition on the walls of the reactors [START_REF] Szopa | PAMPRE: A dusty plasma experiment for Titan's tholins production and study[END_REF]). These products were analyzed using a large set of analytical techniques, including bulk elemental analysis [START_REF] Coll | Experimental laboratory simulation of Titan's atmosphere: aerosols and gas phase[END_REF][START_REF] Szopa | PAMPRE: A dusty plasma experiment for Titan's tholins production and study[END_REF][START_REF] Mcdonald | Chemical Investigation of Titan and Triton Tholins[END_REF][START_REF] Sarker | Titan Aerosol Analogues: Analysis of the Nonvolatile Tholins[END_REF][START_REF] Quirico | New experimental constraints on the composition and structure of tholins[END_REF], pyrolysis [START_REF] Khare | Optical constants of organic tholins produced in a simulated Titanian atmosphere: From soft x-ray to microwave frequencies[END_REF][START_REF] Coll | Experimental laboratory simulation of Titan's atmosphere: aerosols and gas phase[END_REF][START_REF] Szopa | PAMPRE: A dusty plasma experiment for Titan's tholins production and study[END_REF][START_REF] Ehrenfreund | Analytical pyrolysis experiments of Titan aerosol analogues in preparation for the Cassini Huygens mission[END_REF][START_REF] Hodyss | Methods for the Analysis of Organic Chemistry on Titan[END_REF][START_REF] Mcguigan | Analysis of Titan tholin pyrolysis products by comprehensive two-dimensional gas chromatographytime-of-flight mass spectrometry[END_REF]; and laser desorption mass spectrometry experiments [START_REF] Somogyi | Organic environments on Saturn's moon, Titan: Simulating chemical reactions and analyzing products by FT-ICR and ion-trap mass spectrometry[END_REF][START_REF] Ganesan | Analysis of Titan Tholins by Laser Desorption Mass Spectrometry. 38th Lunar and Planetary Science Conference[END_REF][START_REF] Imanaka | Formation of nitrogenated organic aerosols in the Titan upper atmosphere[END_REF] to infrared absorption, visible, UV and near-IR Raman and luminescence spectroscopy [START_REF] Sagan | Polycyclic aromatic hydrocarbons in the atmospheres of Titan and Jupiter[END_REF][START_REF] Mcdonald | Chemical Investigation of Titan and Triton Tholins[END_REF][START_REF] Imanaka | Laboratory experiments of Titan tholin formed in cold plasma at various pressures: implications for nitrogencontaining polycyclic aromatic compounds in Titan haze[END_REF][START_REF] Quirico | New experimental constraints on the composition and structure of tholins[END_REF][START_REF] Khare | Analysis of the time-dependent chemical evolution of Titan Haze Tholin[END_REF][START_REF] Bernard | Reflectance spectra and chemical structure of Titan's tholins: Application to the analysis of Cassini-Huygens observations[END_REF][START_REF] Ruiz-Bermejo | CH4/N2/H2 spark hydrophilic tholins: A systematic approach to the characterization of tholins[END_REF][START_REF] Ruiz-Bermejo | CH4/N2/H2spark hydrophobic tholins: A systematic approach to the characterisation of tholins[END_REF][START_REF] Carrasco | Chemical Characterization of Titan's Tholins: Solubility, Morphology and Molecular Structure Revisited[END_REF])), X-ray diffraction and high resolution transmission electron microscopy [START_REF] Quirico | New experimental constraints on the composition and structure of tholins[END_REF]. A detailed 13 C and 15 N NMR study was performed on tholins synthesized from isotopically labeled N 2 and CH 4 [START_REF] Derenne | New insights into the structure and chemistry of Titan's tholins via 13C and 15N solid state nuclear magnetic resonance spectroscopy[END_REF]. Finally, these compounds present an astrobiological interest due to their ability to release amino acids upon hydrolysis [START_REF] Derenne | New insights into the structure and chemistry of Titan's tholins via 13C and 15N solid state nuclear magnetic resonance spectroscopy[END_REF]) and hydrolysis of various analogues of Titan haze particles in aqueous NH 3 at room temperature for 2.5 years was shown to produce amino acids [START_REF] Cleaves Ii | Amino acids generated from hydrated Titan tholins: Comparison with Miller-Urey electric discharge products[END_REF].

ISM dust

The interstellar medium dust (ISM) is very complex and not at all homogenous in all areas of space. Chemistry in the ISM can be performed in the gas phase or on grains. The dust components play an important role as they shield molecules in the gas phase from the destructive UV radiation field.

The understanding of the chemistry of the ISM is probably one of the most intriguing research subject and many reviews tried to explain the synthesis of the compounds in the medium [START_REF] Jones | The structure and evolution of hydrogenated amorphous carbon grains and mantles in the interstellar medium[END_REF]) Hence, it is very advantageous to reproduce experimental conditions of the reactions which lead to productions of molecules found in the ISM. Until now a lot of effort has been put on the irradiation of ice mixtures comprising small molecules (CO, CO 2 , CH 3 OH, H 2 CO, CH 4 ) that are among the most abundant in the interstellar medium (ISM). In addition, in order to produce more complex molecules likely present in the ISM or in comets [START_REF] Jenniskens | Carbon dust formation on interstellar grains[END_REF][START_REF] Bernstein | The infrared spectra of nitriles and related compounds frozen in Ar and H 2 O[END_REF][START_REF] Schutte | Production of organic molecules in interstellar ices[END_REF][START_REF] Dworkin | An evolutionary connection between interstellar ices and IDPs? Clues from mass spectroscopy measurements of laboratory simulations[END_REF]), these syntheses succeeded in releasing amino acids upon hydrolysis [START_REF] Bernstein | Ultraviolet irradiation of the polycyclic aromatic hydrocarbon (PAH) naphthalene in H2O. Implications for meteorites and biogenesis[END_REF][START_REF] Munoz Caro | Amino acids from ultraviolet irradiation of interstellar ice analogues[END_REF]. Moreover, when a polarized light is used for irradiation, enantiomeric excesses could be measured [START_REF] Nuevo | Enantiomeric separation of complex organic molecules produced from irradiation of interstellar/circumstellar ice analogs[END_REF][START_REF] Danger | Characterization of laboratory analogs of interstellar/cometary organic residues using very high resolution mass spectrometry[END_REF][START_REF] Paola | Enantiomeric Excesses Induced in Amino Acids by Ultraviolet Circularly Polarized Light Irradiation of Extraterrestrial Ice Analogs: A Possible Source of Asymmetry for Prebiotic Chemistry[END_REF]. The other main class of synthesis aimed at identifying the carriers of the infrared bands that are observed in the ISM and these syntheses involved hydrocarbons. Laser pyrolysis of various hydrocarbons (ethylene, acetylene, butadiene and benzene) was shown to produce soluble and insoluble OM, mostly aromatic [START_REF] Galvez | Carbon nanoparticles from laser pyrolysis[END_REF][START_REF] Jäger | Identification and Spectral Properties of Polycyclic Aromatic Hydrocarbons in Carbonaceous Soot Produced by Laser Pyrolysis[END_REF] although the formation of aliphatic carbons upon acetylene pyrolysis could be revealed through FTIR and 1 H NMR [START_REF] Schnaiter | Infrared Spectroscopy of Nano-sized Carbon Grains Produced by Laser Pyrolysis of Acetylene: Analog Materials for Interstellar Grains[END_REF][START_REF] Biennier | Characterization of circumstellar carbonaceous dust analogues produced by pyrolysis of acetylene in a porous graphite reactor[END_REF]).

Combustion of ethylene, acetylene or propylene in O 2 led to the formation of soots [START_REF] Pino | The 6.2 um band position in laboratory and astrophysical spectra: a tracer of the aliphatic to aromatic evolution of interstellar carbonaceous dust[END_REF][START_REF] Carpentier | Nanostructuration of carbonaceous dust as seen through the positions of the 6.2 and 7.7 μm AIBs[END_REF]. Photolysis of a plasma of hydrocarbons at low temperature (10 K) resulted in a so-called hydrogenated amorphous carbon polymer exhibiting a strong aliphatic character and considered as a good analogue for the diffuse ISM organic matter [START_REF] Tokunaga | Quenched Carbonaceous Composite: A laboratory analog for carbonaceous material in the interstellar medium[END_REF][START_REF] Dartois | Diffuse interstellar medium organic polymers[END_REF][START_REF] Dartois | Ultraviolet photoproduction of ISM dust[END_REF]. It must be noted that the aforementioned synthesized materials were further subjected to various treatments (ion or UV irradiation, UV photoprocessing, thermal annealing) to mimic the effects of cosmic rays or the evolution of these materials within molecular clouds or diffuse clouds [START_REF] Jenniskens | Carbon dust formation on interstellar grains[END_REF][START_REF] Strazzulla | Radiation chemistry of ices of planetological interest at low temperature[END_REF][START_REF] Goto | Infrared spectral sequence of quenched carbonaceous composite subjected to thermal annealing[END_REF][START_REF] Godard | Ion irradiation of carbonaceous interstellar analogues[END_REF]. Ice irradiation produced the precursor of amino acids which were also identified upon hydrolysis of meteoritic OM. Irradiation of PAHs in water ice yielded oxidized PAHs similar to some reported in the extracts of meteorites [START_REF] Bernstein | Ultraviolet irradiation of the polycyclic aromatic hydrocarbon (PAH) naphthalene in H2O. Implications for meteorites and biogenesis[END_REF][START_REF] Ashbourn | Ultraviolet photolysis of anthracene in H2O interstellar ice analogs: Potential connection to meteoritic organics[END_REF] but it cannot be excluded that the latter result from aqueous alteration.

Meteorites

The importance of understanding the formation of carbonaceous chondrites is crucial as they contain valuable information regarding the chemical evolution of our Galaxy, down to the possibility of emergence of life on planets. For the last few decades they were extensively analyzed using a great number of different techniques but, up to now, only limited attempts to synthesize organic matter mimicking the one isolated from the chondrites were reported.

Until now, few theories regarding of IOM creation were established. Back in 1977

Hayatsu [START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF] proposed that macromolecular materials are the result of thermallyinduced polymerization and aromatization via Fisher -Tropschtype process which could take place in early solar nebula, involving the catalytic synthesis of hydrocarbons from CO and hydrogen on the grain surface. Later in 1991 Morgan [START_REF] Morgan | A new mechanism for the formation of meteoritic kerogen-like material[END_REF] and his team suggested that the production of chondritic IOM could occur in the solar nebula at high temperature from 900 -1100K. He obtained high molecular weight aromatic structures by gasphase pyrolysis of simple aliphatics such as acetylene and methane. Recently, Callahan [START_REF] Callahan | Irradiated benzene ice provides clues to meteoritic organic chemistry[END_REF] described the synthesis of a series of polyphenyl compounds upon benzene irradiation. The same compounds were shown to be present, although in trace amounts, in the organic extract of Murchison meteorite. Other effort has been described by [START_REF] Kuga | Synthesis of refractory organic matter in the ionized gas phase of the solar nebula[END_REF] reporting the synthesis of solid organics under ionizing conditions in a plasma setup from gas mixtures H 2 (O)-CO-N 2 -noble gases).

They consider that trapped noble gases in IOM which share similarities with IOM isolated from chondrites might not have required a cold environment and could have occurred anywhere where the disk is ionized, including in its warm regions.

As stressed above, synthesizing chemical structures similar to the organics isolated from carbonaceous chondrites is therefore a major challenge.

Most important issues-what can be done?

As I have mentioned in the previous chapter that establishing the organic chemical constitution of our Solar System before the origin of life is a fundamental goal. Hence the synthesis of the organic matter similar to organic matter isolated from carbonaceous chondrites is crucial.

The aim of most studies, described in the previous paragraph, which considers different kind of synthesis of extraterrestrial bodies is the search for spectroscopic signatures of synthetic materials produced in circumstellar or interstellar conditions.

However, as far as the solid phase is concerned, a unique molecular structure can rarely be unambiguously attributed to spectroscopic signatures. In the case of the IOM isolated from meteorites, this issue is circumvented since the combination of various available laboratory techniques gives an access to its chemical structure at the molecular level. The aim of the research described in this thesis is, via multiple analytical approaches that have already given successful results on natural samples, to reconstruct the molecular structure of the polyaromatic IOM condensed from aliphatic hydrocarbons or/and N and O containing organic compounds submitted to a radio frequency plasma discharge. The main goal is to search the synthetic route of the meteorite IOM based on its molecular structure [START_REF] Derenne | Model of molecular structure of the insoluble organic matter isolated from Murchison meteorite[END_REF]. The experimental conditions can be transposed to the conditions prevailing at the surface of the circumsolar T-Tauri disk, where ion chemistry and photochemistry took place simultaneously at the very early stage of the solar system formation [START_REF] Willacy | Deuterium Chemistry in Protoplanetary Disks[END_REF].

Materials and methods

All the syntheses were performed in the Mineralogy and Cosmochemistry

Laboratory in National Museum of Natural History in Paris where the vacuum line designed by F. Robert is located. Secondary produced organic matter is extracted and analyzed in the Laboratory METIS under the supervision of S. Derenne at University Pierre et Marie Curie using the same set of techniques which were implemented previously for the analysis of Murchison and Orgueil chondrites.

Synthesis of organic matter

Syntheses were performed using a vacuum line into which an organic precursor is submitted to microwave discharge thus creating an organic plasma.

Plasma basics

Plasma, which is used in the synthesis of organic matter, is the fourth state of matter, aside from the solid, liquid and gaseous states and it corresponds to its most disordered state. Plasma is an ionized gas meaning that at least one electron is not bound to an atom, converting the atoms into positively charged ions, which make the plasma electrically conductive, internally interactive [START_REF] Fridman | Plasma Chemistry[END_REF]. Plasma can be created by heating of the gas or subjecting it to a strong electromagnetic field applied with a laser or microwave generator. A radiofrequency discharge, as used in the present vacuum line for the synthesis, increases the number of electrons thanks to collisions with atoms of the gas which are injected to the line. The repetitive effect causes the number of electrons to grow significantly over short periods of time, an effect which is known as an "avalanche". The energetic electrons bump into atoms of introduced gas particles, exciting them from the ground electronic states to higher energy levels. The excitation energy is then released as UV radiation as seen on the image below. In the present work, the microwave plasma is used as a source of UV irradiation of organic compounds and energetic electrons which are highly reactive.

Description of the synthesis device

A high vacuum (up to ~3 x 10 -4 mbar) glass line similar to the so-called Nebulotron (Robert et al., 2011) is used for the syntheses. It is equipped with two pressure gauges in order to control the pressure of the gases on the way in and way out of the reaction (Fig. 2.1). The glass line is fitted with turbo molecular secondary and primary pumps on the way out as all the experiments are made during the constant flow of the gases. The device, includes a removable U-shaped Pyrex tube where the synthesis takes place (Fig. 2.2). 2 ml of substrate is transferred into the vacuum chamber in the form of gas. In all cases the substrates are the purest available chemicals ≥99% purchased from Sigma-Aldrich (fully deuterated 99,5% pentane, n-pentane, n-octane, hexylamine and ethanol) and Air Liquide (N 2 ). The irradiation is performed with Evenson cavity [START_REF] Fehsenfeld | Microwave discharge cavities operating at 2450 MHz[END_REF] used to excite microwave discharges with 2450 MHz microwave generator (Opthos Instruments). In the absence of refrigeration, the temperature of the reaction, measured on the outer surface of the Pyrex glass, rises up to 72 °C. It must be noted that the nature of the synthesis does not allow measuring the actual temperature of the gas inside the reaction vessel. The pressure during the synthesis is maintained at 3 mbar and the reflected power on the microwave generator is close to 0 watt. Before each experiment, the high vacuum glass line is cleared from any possible contaminants coming from the air and solvents. To this end, the entire system is heated to 100°C The synthesized material was further extracted with a mixture of dichloromethane and methanol, 2:1, v:v. The soluble organic matter (SOM) is separated from the insoluble residue (IOM) through centrifugation for 30 min at 12000 rpm. The supernatant is further concentrated using rotary evaporation. SOM was weighed after separation.

2.2 Soluble organic matter analysis SOM is analyzed using gas chromatography/mass spectrometry (GC/MS). This technique which combines two analytical methods allows the identification and quantification of volatile compounds in complex mixtures. eV, ion source temperature 220°C scanning from 40-700 amu at 2.24 scan.s -1 .

Insoluble organic matter analysis

After having determined its bulk chemical composition through elemental analysis, the synthesized IOM was analyzed through several spectroscopic (FTIR, Raman, NMR, EPR) methods along with thermal (Pyrolysis-GC-MS) and chemical (RuO 4 oxidation) degradations. Nanoscale analyses were also performed through HRTEM and NanoSIMS.

Elemental analysis

The elemental composition (carbon, hydrogen, nitrogen and oxygen) was performed on IOM. In order to remove possible traces of water or solvent which was used in the extraction process, samples were dried for 24h in a desiccator beforehand. Analysis has been completed at the Institut des Sciences Analytiques in Villeurbanne (France).

FTIR

Infrared spectroscopy is based on the radiation absorption at specific frequencies characteristic of chemical bonds. The electromagnetic wavelength range is between 4000 cm -1 and 400 cm -1 . Two types of vibrations in bonds can be distinguished:

-A stretching mode of oscillations (shortening and lengthening of the bond with a particular amplitude and frequency)

-A deformation mode (changing the angle between a bond and a given part of the molecule In complex molecules, the IR spectrum comprises numerous bands related to the various vibrational modes as illustrated in Fig. 2.4.

Fig. 2.4 Example of FTIR spectrum of organic molecule (octene)

Fourier transform infrared spectrophotometer (FTIR) allows measuring simultaneously all the infrared frequencies through the use of an interferometer. This type of device reduces the analysis time of several minutes to a few seconds.

Nevertheless the original information requires the development of a mathematical process known as Fourier transform.

In the present work, the IOM was analysed as KBr pellets. FTIR spectra were recorded using a Bruker Tensor 27 spectrometer. The spectra (32 scans) were recorded after pellet desiccation at room temperature for 4 hours.

Raman Micro-spectroscopy

Raman spectroscopy is a spectroscopic technique used to observe vibrational, rotational, and other low-frequency modes in a system. In this analysis, photons from a monochromatic light (laser) are focused onto a sample and when interacting with a molecule, they are either reflected, absorbed or scattered. Raman spectroscopy is the study of the influence of light on matter where the light is inelastically scattered.

This inelastic scattering is called the Raman effect. Not every molecule or functional group exhibits Raman scattering. Factors such as the polarization state of the molecule (which determines the Raman scattering intensity) must be considered. The greater the change in polarizability of the functional group, the greater the intensity of the Raman scattering effect. This means that some vibrational or rotational transitions, which exhibit low polarizability will not be equally Raman active, will not appear in a Raman spectrum. In Raman micro spectroscopy, the micro spectrometer is used in place of a standard one. This allows acquiring spectra of microscopic samples or microscopic areas of larger samples.

When carbonaceous materials are considered, Raman spectra typically exhibit two main bands G and D (Fig. 2.5) corresponding to 1580 cm -1 and 1350 cm -1 respectively. As proposed by Sadezky [START_REF] Sadezky | Raman microspectroscopy of soot and related carbonaceous materials: Spectral analysis and structural information[END_REF], Raman spectra can be decomposed into a combination of 5 Lorentzian/Gaussian bands (namely, D1, D2, D3, D4 and G). Then, various Raman parameters can be determined, the Full Width at Half Maximum of the D1 (FWHM-D1) and of the G (FWHM-G) bands and the intensity (band height) ratio of D1 and G bands, termed R1 ratio [START_REF] Lahfid | Evolution of the Raman spectrum of carbonaceous material in low-grade metasediments of the Glarus Alps (Switzerland)[END_REF].

Moreover, in some cases, an additional sixth band (D5) is required [START_REF] Rouzaud | Carbons at the heart of questions on energy and environment: A nanostructural approach[END_REF]. Like NMR, it is based on the transition between degenerate spin states although electrons are considered instead of nuclei and EPR the radiation is in the gigahertz and radiation is held constant when magnetic field is varied in order to obtain an absorption spectrum. Three parameters are commonly derived from EPR spectra (Fig2.7):

-the g factor which is directly related to the chemical composition of the radicals -the peak-to-peak amplitude (A) which is proportional to the number of spins and thus to the radical concentration in the sample -the linewidth (B) which provides information on the diversity of radicals When macromolecules comprising polar moieties are investigated, their pyrolysis products may not be GC-amenable and thus need to be derivatized. To this end, an in situ methylation is achieved using tetramethylammonium hydroxide (TMAH). The latter, which is also a base reagent, both induces the preferential cleavage of ester bonds and releases more volatile methylated counterparts of pyrolysis products.

Thus the 4mg of analyzed sample is mixed with 18ml of 25% solution of TMAH in methanol in order to obtain 1/1 proportion in mass of analyzed sample to TMAH. The thus impregnated sample is then placed in the ferromagnetic wire.

Ruthenium Tetroxide Oxidation (RuO 4 oxidation)

RuO 4 oxidation is a mild oxidation which is especially efficient to release the aliphatic linkages between aromatic moieties. The experimental conditions were based on previously published oxidation of Murchison and Orgueil meteorite (Remusat et al. 2005a). A mixture of 1 mL of CH 2 Cl 2 2 mL of distilled water, 1 mL of CH 3 CN, 500 mg of sodium metaperiodate (Sigma-Aldrich), and 50 mg of sample were stirred for 30 min at room temperature. Then 5 mg of ruthenium (IV) dioxide (Sigma-Aldrich) were added followed by constant stirring. After 4 h, few drops of isopropanol were added to stop the reaction, then after 5 min the residue was separated by filtration and successively rinsed with 10 ml of MeOH, 20 ml of CH 2 Cl 2 , and 20 ml of distilled water. The organic filtrates were dried over sodium sulfate. The aqueous filtrate was extracted with ether and combined with the organic filtrates. This organic solution was concentrated by rotary evaporation and dried under N 2 at room temperature prior to silylation which is automatically performed in the GC autosampler by heating up 100 µl of solution with 10 µl N,O-Bis(trimethylsilyl)trifluoroacetamide (BSTFA) for 10 min at 60°C.

An aliquot of the organic solution was also methylated by refluxing it into 15 ml of MeOH for 1h in the presence of few drops of acetyl chloride [START_REF] Quénéa | Spectroscopic and pyrolytic features and abundance of the macromolecular refractory fraction in a sandy acid forest soil (Landes de Gascogne, France)[END_REF].

Silylated ethers and methyl esters were analyzed using GC-MS with the aforementioned experimental conditions (2.2). Procedural blank experiments, with and without standard diacids (succinic, glutaric, and adipic acids), were carried out to rule out any laboratory pollution among the oxidation products and check that no short products are lost during the analytical procedure.

HRTEM

High resolution transition electron microscope (HRTEM) is an instrument for highmagnification studies. High resolution makes it ideal for imaging materials on the atomic scale. Main benefit of a TEM over other microscopes is that it can give information in real space (imaging mode) and reciprocal space (diffraction mode) in the same time.

The basic principle of TEM is quite similar to the optical microscope although a focused beam of electrons is used instead of light to "image" and obtain information about the structure and composition of the sample. An electron source -the "gun" produces a stream of electrons which are accelerated toward the sample using a positive electrical potential. This stream is then focused using metal apertures and magnetic condenser lenses into a thin, focused, monochromatic beam, a part of which being transmitted through the sample (Fig. 2.9). This portion of the beam is Analogically, the D/H ratio and the ionic intensities of C -, CH -, CH 2-, and CH 3- were recorded with the mass spectrometer in 20x20 µm 2 images divided in 9 Regions

Of Interest (ROI 45 µm 2 ). The isotopic ratios of these ROI are expressed in D (‰)

relative to the bulk D/H ratio of the organic residues (calculated from 371 individual ROI defining a 2 sigma error domain of ±110‰). The kerogen and charcoal were the analytical standards used in the analysis.

3 Synthesis of organic matter containing carbon and hydrogen

Introduction

Carbonaceous meteorites are fragments broken from small bodies that have remained fairly unprocessed, surviving their fall on Earth from space. These objects contain up to 4% of carbon. Most of this carbon occurs as organic matter, which comprises a large diversity of extraterrestrial organic molecules along with macromolecular insoluble organic matter (IOM) (Robert andEpstein 1982, Cronin andChang 1993). The analysis of the chemical composition of the meteoritic organic matter has been mainly focused on the Murchison meteorite over the last three decades. The chemical structure of the IOM was recently investigated using a combination of analytical approaches including various spectroscopic methods [START_REF] Cronin | 13C NMR spectroscopy of the insoluble carbon of carbonaceous chondrites[END_REF][START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF], Binet et al. 2002[START_REF] Cody | Solid-state (1H and 13C) nuclear magnetic resonance spectroscopy of insoluble organic residue in the Murchison meteorite: a self-consistent quantitative analysis[END_REF], Binet et al. 2004[START_REF] Cody | NMR studies of chemical structural variation of insoluble organic matter from different carbonaceous chondrite groups[END_REF][START_REF] Orthous-Daunay | Speciation of sulfur in the insoluble organic matter from carbonaceous chondrites by XANES spectroscopy[END_REF], thermal and chemical degradations followed by gas chromatography coupled with mass spectrometry (GC-MS), [START_REF] Studier | Origin of organic matter in early solar system-V. Further studies of meteoritic hydrocarbons and a discussion of their origin[END_REF][START_REF] Levy | The organic analysis of the murchison meteorite[END_REF][START_REF] De Vries | A search for C60 in carbonaceous chondrites[END_REF][START_REF] Sephton | Aromatic units from the macromolecular material in meteorites: Molecular probes of cosmic environments[END_REF][START_REF] Sephton | Organic matter in ancient meteorites[END_REF][START_REF] Sephton | Small-scale hydrous pyrolysis of macromolecular material in meteorites[END_REF], Remusat et al. 2005a, Remusat et al. 2005b) along with high-resolution transmission electron microscopy (Derenne et al. 2005).

Taken together, all the data derived from the aforementioned analytical methods led to propose a model of molecular structure for the IOM of Murchison (Derenne and Robert 2010) which has been already discussed in the chapter "State of the Art". The aim of the study in this chapter is to test experimentally this mechanism by synthesizing an analogue to the hydrocarbon skeleton of the meteorite IOM. This can be considered as a first step towards the synthetic route of the meteorite IOM.

A few attempts to synthesize analogues of extraterrestial organic matter have been reported so far. They often aim at reconciling the spectroscopic observations on astrophysical media with those obtained on synthetic organic matter. Various targets were distinguished in the literature such as cometary ices, interstellar organic molecules (on grains or in the gas phase), interplanetary dust particles (IDPs), meteorites, or Titan's aerosols and they were described earlier in this thesis. When the meteorite field is concerned, only limited syntheses of their analogues were published. Only recently, Callahan et al. [START_REF] Callahan | Irradiated benzene ice provides clues to meteoritic organic chemistry[END_REF] reported the synthesis of a series of polyphenyl compounds upon benzene irradiation. The same compounds were shown to be present, although in trace amounts, in the organic extract of Murchison meteorite.

Fortunately, in the case of the IOM isolated from meteorites, the combination of various available laboratory techniques gives an access to its chemical structure at the molecular level. In the present study, we used this multiple analytical approach that has already given successful results on natural samples, to characterize the molecular structure of synthesized OM The synthesis conditions can be transposed to the conditions prevailing at the surface of the circumsolar T-Tauri disk, where ion chemistry and photochemistry take place simultaneously [START_REF] Willacy | Deuterium Chemistry in Protoplanetary Disks[END_REF].

Aliphatic hydrocarbons are submitted to a radio frequency plasma discharge so as to yield short radicals which can then react together. The thus formed OM was analyzed by GC-MS for its soluble part and contamination issues were addressed using a deuterated precursor. The chemical structure of the synthesized IOM was compared with that of Murchison through pyrolysis coupled with GC-MS, ruthenium tetroxide (RuO 4 ) oxidation, solid state 13 C NMR, FTIR, HRTEM, Raman micro-spectroscopy, EPR and NanoSIMS.

Two types of hydrocarbons were used as precursors in these syntheses, octane and pentane, on the one hand, and methane, on the other hand. Whereas higher yields are obtained with octane and pentane than methane, the latter was used to check the proposed mechanism as its plasma chemistry is well documented. This chapter comprises two parts corresponding to the two types of precursors.

3.2 Chemical structure of OM synthesized from pentane or octane *

Synthesis

The total yield of synthesized material ranges from 0.3 to 15 % depending on the synthesis parameters (Table 3.1). An increase in temperature, power and reaction time as well as the use of octane instead of pentane, i.e. the increase in C number of the alkane precursor, result in an increase in the yield. The maximum yield, 15 wt %, is thus obtained after 60 min of irradiation using n-octane as a precursor at 60 watts forced power at 72 °C (Table 3.1). Under these conditions, the soluble and insoluble organic matter is produced in the ratio of 15:85. GC-MS and pyrolysis GC-MS analyses further indicate that the different factors influence the yield of the reaction but do not have any noticeable impact on the chemical structure of the synthesized products. * -temperature of the glass surface of the reaction tube

Contamination issue

Before a detailed analysis of the synthesized OM, the contamination had to be addressed. Syntheses performed using deuterated and unlabeled n-pentane under the same conditions led to similar results as shown by the two GC-MS traces of the soluble fractions (Fig. 3.1).

Characterization of the soluble OM by GC-MS

All the identified compounds in the soluble fraction (Fig. 3.3, Table 3.2) correspond to polycyclic hydrocarbons with two (1-4,6) to five rings (24-26), the most abundant being phenanthrene (15) and pyrene (21). In addition to the parent compound themselves, some counterparts bearing short alkyl substituents (C 1 -C 3 ) are also identified. The composition of the soluble fraction obtained after octane irradiation shows that the fragmentation of the aliphatic precursor leads to the formation of aromatic compounds, thus supporting the proposed mechanism. In addition, the similarity in chemical composition of the soluble OM formed under various conditions (time, temperature, precursor chain length and forced power of the microwave generator) suggests that the first step in the synthesis involves the breakdown of the precursor into small units. More especially, it must be noted that the increase in yield between the synthesis performed from pentane and octane likely only reflects an increase in the number of such units. It has been checked that there is no trace of octane left in the products, indicating that the precursor is completely cleaved in the plasma. More generally, no aliphatic compound could be detected.

650°C Pyrolysis-GC-MS analysis of the IOM

Pyrolysis-GC-MS is commonly used to study macromolecular OM in terrestrial samples like kerogens and coals but also in extraterrestrial samples such as meteorites (Remusat et al. 2005b[START_REF] Murae | Characterization of extraterrestrial high-molecular-weight organic matter by pyrolysis-gas chromatography/mass spectrometry[END_REF][START_REF] Komiya | Organic compounds from insoluble organic matter isolated from the Murchison carbonaceous chondrite by heating experiments[END_REF][START_REF] Okumura | Gradual and stepwise pyrolyses of insoluble organic matter from the Murchison meteorite revealing chemical structure and isotopic distribution[END_REF][START_REF] Sephton | Aromatic units from the macromolecular material in meteorites: Molecular probes of cosmic environments[END_REF]) and tholins [START_REF] Szopa | PAMPRE: A dusty plasma experiment for Titan's tholins production and study[END_REF][START_REF] Khare | Organic solids produced by electrical discharge in reducing atmospheres: Tholin molecular analysis[END_REF][START_REF] Mcguigan | Analysis of Titan tholin pyrolysis products by comprehensive two-dimensional gas chromatographytime-of-flight mass spectrometry[END_REF]). The IOM synthesized in the present study was therefore analyzed using Curie point pyrolysis. The pyrochromatogram shows a large number of peaks (Fig. 3.4).

Pyrolysis products (Table 3.3) are aromatic compounds comprising one (1-7, 11, 12) to four rings (29, 30). The abundance of the products seems to decrease with the number of rings suggesting a rather small size for the aromatic units in the macromolecule. Most compounds bear short alkyl substituents (2-7, 10-13, 15-18, 20, 23, 26). A lack of predominance of specific isomers is also observed among all pyrolysis products.

The pyrolysate of the synthesized IOM only comprises cyclic, mainly aromatic products. It cannot be excluded that at least a part of these products underwent cyclization and aromatization upon pyrolysis and thus were not preexisting in the IOM. Such an artifact should be rather limited as the soluble fraction also exhibits a strong aromatic character and that soluble and insoluble fractions are expected to represent a continuum in molecular weight and cross-linking. However, to address this question, the IOM was submitted to a pyrolysis at a lower temperature, where the C-C cleavages are limited and products are mainly released through thermodesorption.

358°C Pyrolysis-GC-MS analysis of the IOM

The 358°C pyrolysate was analyzed by GC-MS as the 650°C one and the soluble OM (Fig. 3.3, Table 3.2). Comparison between the traces (Figs 3.3 and 3.4) shows that the heaviest compounds released at 358°C were also present in the SOM fraction as well as in the 650°C pyrolysate. This definitely shows that they are not formed through cyclisation/aromatization upon high temperature pyrolysis but that they originate, at least partly from thermodesorption. The low molecular weight compounds were not detected in the SOM as they are likely lost upon SOM concentration prior to GC-MS analysis. However, most of them were present in the 650°C pyrolysate also suggesting their trapping within the organic macromolecular network. Only two compounds were missing in the 650°C pyrolysate, heptane and octane. These aliphatic hydrocarbons are the main left-over products of the synthesis, octane being the reagent itself and heptane the first derived hydrocarbon (through loss of one carbon atom). It is likely that shorter aliphatic hydrocarbons also contribute to the 358°C pyrolysate but they are too volatile to be detected in the presently used GC conditions. The aromatic products released at 358°C corresponded to the most abundant 650 °C pyrolysis products. However, some products of the 650°C pyrolysate were not detected in the 350°C one. Taken together, these observations show that the compounds in the 650°C pyrolysate are derived from both the actual cracking of the macromolecular network and the thermodesorption of trapped products within the organic network. This clearly supports their presence as aromatic moieties of the IOM and rules out any significant formation through cyclization/aromatization. However, due to limitations in GC-MS, one cannot derive from the 358°C and 650°C pyrolysis data an actual distribution of the size of the aromatic units existing in the synthesized IOM. This can be achieved through HRTEM which provides a direct observation of the polyaromatic unit profile and allows semi quantification using image analysis (Rouzaud andClinard 2002, Le Guillou et al. 2012).

HRTEM observation of the IOM

HRTEM images of the synthesized IOM point to rather weak organization of the aromatic units (short and disoriented fringes, large interlayer spacing, very small coherent domains). However, two different types of nanostructure can be distinguished, namely amorphous-like particles (Fig. 3.5 a, b) and disordered carbon areas characterized by longer fringes (Fig. 3.5 c, d). These two different areas could reflect structural heterogeneity of the sample possibly related to wall effect during the synthesis. Semi-quantitative structural data were obtained after skeletonization of HRTEM images [START_REF] Rouzaud | Quantitative high-resolution transmission electron microscopy: a promising tool for carbon materials characterization[END_REF]. The length of all fringes, interlayer spacing and percentage of single layers was individually measured. Average values resulting from hundreds of fringes are reported in Table 3.5. They confirm the very small size of the polyaromatic structures as well as their very low level of organization. Indeed, their size ranges between 0.39 and 0.48 nm corresponding to 1 -4 rings. Most of the layers are not stacked to form coherent domain and can be considered as single layers. The mean interlayer spacing is large, far from the 0.3354 nm for perfect graphite. The low level of organization observed through HRTEM is consistent with the features highlighted by GC-MS and Py-GC-MS, the high level of substitution likely preventing the formation of large polyaromatic units as well as their stacking to form coherent domains (a majority of the nonstacked layers is observed even in the less disordered carbon, Table 3.5).

Raman Micro-spectroscopy analysis of the IOM

Raman microspectroscopy was implemented so as to derive quantitative information on the "mean" structure of these carbonaceous deposits. This vibrational spectroscopy is sensitive not only to crystal structure but also to the structure of disordered carbons [START_REF] Sadezky | Raman microspectroscopy of soot and related carbonaceous materials: Spectral analysis and structural information[END_REF], Rouzaud et al. 2015). Such disordered carbons are characterized by two main broad bands "G" at about 1600 cm -1 , corresponding to the graphite E2g mode and "D" at 1350 cm -1 attributed to different types of defects (Sadezky et al. 2005, Tuinstra and[START_REF] Tuinstra | Raman Spectrum of Graphite[END_REF].

In the synthesized IOM, four types of spectra can be recognized (Fig. 3.6).

Although all the spectra exhibit the two broad bands of disordered carbons, two groups of spectra can be distinguished based on the baseline which can be oblique (spectra A and B) or not (spectra C and D). This is due to a strong fluorescence emissions, usually attributed to the presence of aliphatic units in the macromolecular network [START_REF] Romero-Sarmiento | Evolution of Barnett Shale organic carbon structure and nanostructure with increasing maturation[END_REF]. In this case, the bands, and especially the D one, are very large (see spectrum A), and the D/G ratio rather low. This type of spectrum corresponds to the "amorphous-like" carbons detected by HRTEM. Note, however, that true amorphous carbons, i.e. made of randomly distributed carbon atoms, would give a spectrum with only a single very broad band, maximizing at 1530 cm -1 . The second type of spectra (C and D) is commonly observed for disordered carbonaceous materials [START_REF] Rouzaud | Carbons at the heart of questions on energy and environment: A nanostructural approach[END_REF]. When compared to the previous type, their band widths are smaller and their D/G ratio higher. The difference between the two types likely reflects difference in the carbonization degree in the synthesized material [START_REF] Romero-Sarmiento | Evolution of Barnett Shale organic carbon structure and nanostructure with increasing maturation[END_REF], Rouzaud et al. 2015). These Raman observations are consistent with the HRTEM data which also differentiated two types of carbonaceous matter. The disordered part which is the major phase in the "macromolecular" material is slightly more ordered and probably devoid of a hydrocarbon component. The difference in carbonization degree could be related to vessel wall effects, some polyaromatic molecules being deposited parallel to the surface.

NMR analysis of the IOM

All the above-described data were unable to reveal any aliphatic contribution to the IOM, except the short aliphatic substituents of the aromatic pyrolysis products.

Similar observations were made on meteoritic IOM despite a significant signal in 13 C NMR. Indeed, 13 C NMR differentiates the 13 C nuclei based on their chemical environments, giving an indication of the overall carbon composition.

Solid state 13 C NMR has been applied to numerous types of natural IOM such as coals [START_REF] Erdenetsogt | Solid-state C-13 CP/MAS NMR study of Baganuur coal, Mongolia: Oxygen-loss during coalification from lignite to subbituminous rank[END_REF][START_REF] Yoshida | Prediction of coal liquefaction reactivity by solid state 13C NMR spectral data[END_REF] and oil shales [START_REF] Maciel | Comparison of oil shales and kerogen concentrates by 13C nuclear magnetic resonance[END_REF][START_REF] Miknis | Cross polarization magic-angle spinning 13C NMR spectra of oil shales[END_REF][START_REF] Miknis | 13C NMR measurements of the genetic potentials of oil shales[END_REF]) but also extraterrestrial samples, like meteorites [START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF][START_REF] Cronin | 13C NMR spectroscopy of the insoluble carbon of carbonaceous chondrites[END_REF][START_REF] Cody | NMR studies of chemical structural variation of insoluble organic matter from different carbonaceous chondrite groups[END_REF][START_REF] Remusat | The insoluble organic matter in carbonaceous chondrites: Chemical structure, isotopic composition and origin[END_REF] or tholins [START_REF] Derenne | New insights into the structure and chemistry of Titan's tholins via 13C and 15N solid state nuclear magnetic resonance spectroscopy[END_REF]. It involves the so-called 1 H-13 C cross polarization (CP) sequence for sensitivity enhancement and magic angle spinning (MAS) to reduce peak broadening.

The spectrum of the synthesized IOM, recorded with a classical contact time t c of 3 ms, shows two main peaks assigned to aliphatic and aromatic carbons (Fig. 3.8). In order to acquire quantitative data, 12 spectra were recorded with a contact time t c ranging from 100 to 9000 µs (Fig. 3.9a). It must be noted that the smaller peaks and shoulders are hardly visible at the shortest t c due to inefficient magnetization transfer from H to C. This reflects either the lack of H on the considered C (139 pm peak) or the molecular motion in the methyl groups (14 and 22 ppm peaks). The evolution of the shape of the spectrum with t c thus clearly emphasizes the necessity to record spectra at various t c to derive quantitative data. The latter can be obtained by plotting the intensity I of each signal vs t c as it is known that, at long t c , it follows the equation ( 1),

𝐼 = 𝐼 0 𝑒 -𝑡 𝑐 𝑇 1𝜌𝐻 ⁄ (1)
where I 0 is proportional to the number of C contributing to that signal and T 1ρH is the spin-lattice relaxation time. I 0 can be determined from the intercept in a Ln I = f(t c ) diagram (Fig. 3.9b). The obtained values for the 5 types of C are gathered in Table 3.6 and reveal a significant contribution of aliphatic carbons. 3.2.9 FTIR analysis of the IOM FTIR is a spectroscopic method which provides complementary information to NMR. When applied to the synthesized IOM, it confirms the presence of aliphatic chains through the bands around 2900 cm -1 (aliphatic C-H stretching absorptions)

and 1450 and 1375 cm -1 (asymmetrical CH 2 and CH 3 and symmetrical CH 3 bending vibrations, respectively) although the spectrum also exhibits bands at 1600 cm -1 (C=C in plane vibrations) and between 700 and 900 cm -1 (C-H out of plane deformations) (Fig. 3.10). Moreover, the relative intensities of the 1450 and 1375 cm - 1 bands point to a significant contribution of methyl groups in the aliphatic C, in agreement with NMR calculations. However, no molecular information on the aliphatic carbons (chain length, branching level) can be deduced from these spectroscopic data and RuO 4 oxidation had to be performed. The oxidation products of the synthesized IOM are analyzed after silylation. They mainly comprise aliphatic mono-and dicarboxylic acids along with small amounts of aromatic acids (Fig. 3.11, Table 3.7). Monocarboxylic acids (1-5, 9-11, 14, 20, 21, 23) indicate the presence of alkyl chains linked to an aromatic ring and diacids (7, 16-18, 22, 24-26, 28, 29) reflect an alkyl bridging between two aromatic units. It must be noted that diacids are less abundant than monoacids. The monocarboxylic acids ranged between C 5 (1-5) to C 10 ( 23), showing that the chain length of the substituent comprises 4 to 9 carbon atoms. As for the diacids, their total chain length ranges from C 2 to C 9 (maximum C 6 ) leading to aliphatic linkages up to 7 carbon atoms. It must be noted that no propanedioic acid (C 3 ) could be detected, likely due to its degradation into CO 2 and formic acid under the experimental conditions as previously suggested by Stock and Wang (1986). Numerous isomers are observed in both mono-and diacids pointing to a high branching level in these aliphatic chains. Two cycloalkane carboxylic acids are detected with C 5 and C 6 rings (6, 15) as well as a series of -1 oxocarboxylic acids ranging from C 5 to C 7 (8,12,19). The formation of such ketoacids was reported through oxidation of the double bond in substituted cycloalkenes (Coudret et al., 1996;Reiss et al., 1997;Zimmermann et al., 2005). The presence of such structures is consistent with a weak band at 1680 cm -1 in the FTIR spectrum (Fig. 3.10). Taken together, these two types of compounds point to the presence of non-aromatic rings in the IOM, consistently with the presence of indane, indene or dihydronaphthtalene derivatives in the IOM pyrolysate. Aromatic acids comprise benzoic acid ( 13) along with two isomers of benzenedicarboxylic acid ( 27), which arise from the oxidation of fused benzene rings in polyaromatic units.

To go further in the identification of the IOM oxidation products, they were also analyzed after methylation.

GC-MS analysis of methylated RuO 4 oxidation octane product

The methylated IOM oxidation products were analyzed by GC-MS.(Fig. 3.12, Table 3.8). Although the TIC trace of the methylated products (Fig. 3.12) looks quite different from that of the silylated products (Fig. 3.11), owing to differences in both retention times and ionization ability, most of the IOM oxidation methylated products were previously detected as their silylated homologues (Table 3.7). They mainly comprise aliphatic (C 5 to C 9 ) and aromatic dicarboxylic acids. However, aliphatic tricarboxylic acids comprising 6 and 7 carbon atoms could be revealed by this derivatization whereas only dicarboxylic acids were observed in the silylated products. The occurrence of these tricarboxylic acids reveals that aliphatic linkages between aromatic units are branched and that one chain can link several aromatic units. Similarly, two benzenetricarboxylic acids could be detected as their methylesters. They likely correspond to 1,2,3-and 1,2,4-benzene tricarboxylic acids because these compounds are known to arise from the oxidation of naphthalene, phenanthrene, and other more complex polycyclic aromatic substances (Stock and Wang, 1986). These polycarboxylic aromatic acids thus likely reflect the oxidation of polyaromatic units.

* -contaminants (phthalates) Fig. 3.12 TIC of RuO 4 oxidation products of the IOM upon methylation procedure. The acids are detected as their methyl esters. Numbers refer to Table 3.8 [START_REF] Binet | Heterogeneous distribution of paramagnetic radicals in insoluble organic matter from the Orgueil and Murchison meteorites[END_REF](Binet et al , 2003;;[START_REF] Gourier | Extreme deuterium enrichment of organic radicals in the Orgueil meteorite: Revisiting the interstellar interpretation[END_REF], Delpoux et al 2010) showing that the highly aromatic structure contains free organic radicals enriched in deuterium, which are concentrated in micro regions in contrast to terrestrial samples.

Moreover their spin concentration depends on the temperature whereas in terrestrial samples the spin concentration is temperature independent. Thus to compare with the meteorite IOM, the effect of temperature on the molecular magnetism was investigated on the synthesized IOM from octane.

The EPR spectrum recorded at room temperature exhibits two signals: a sharp one (marked A) with peak-to-peak linewidth ∆Bpp≈0.7 G and a broader one (marked B) with ∆Bpp≈4 G (Fig. 3.13). The linewidth of signal A is close to those measured for radicals in Precambrian cherts, while the width of signal B is close to those of radicals in carbonaceous chondrites [START_REF] Binet | Heterogeneous distribution of paramagnetic radicals in insoluble organic matter from the Orgueil and Murchison meteorites[END_REF] or in phanerozoic cherts (Skrzypczak-Bonduelle et al., 2008). The broader width for signal B may be related to a larger disorder among radicals responsible for signal B, or to a higher content in hydrogen, which induces a broadening due to unresolved hyperfine interaction. The two distinct signals in the EPR spectrum clearly indicate the existence of two populations of radicals with distinct structural features. However, the EPR linewidth alone cannot be used to infer any structural similarity between the radicals in the present samples and those detected whether in cherts or in carbonaceous chondrites. The g-factor of the synthesized IOM, which is sensitive to the electronic structure of the radicals, was deduced from the field position of the line, and equals 2.0026 ± 0.0004 which is very close to the global g-values from Orgueil and Murchison, 2.00312 ± 0.0005 and 2.00310 ± 0.0004 respectively. The slightly lower g-value for the synthesized IOM compared to those for meteoritic IOM is consistent with a lower content of heteroelements in the radicals of the synthesized IOM as the latter was only produced from C and H atoms. Furthermore the radical concentration of the synthesized IOM is relatively small but quite close to the values calculated from

Orgueil and Murchison meteorites with (5±0.8) x 10 18 spin.g -1 to be compared with

(1.8±0.3) x 10 18 spin.g -1 and (7±0.8) x10 18 spin.g -1 for Orgueil and Murchison IOM, respectively [START_REF] Binet | Heterogeneous distribution of paramagnetic radicals in insoluble organic matter from the Orgueil and Murchison meteorites[END_REF].

Fig. 3.13 EPR spectrum at room temperature of the synthesized IOM from octane.

Indirect information about the nature of paramagnetic species can also be acquired from the variation of the EPR intensity (which is proportional to the magnetic susceptibility) with temperature. The EPR measurements were carried out from the 4 K temperature and the quality factor of the EPR cavity was checked to be constant over the change of temperature to make sure that changes in intensities are intrinsic to the sample and not related to changes in instrumental characteristics or dielectric losses in the sample. Fifteen EPR spectra were recorded at a sufficiently low microwave power (P=0.2 mW) to avoid saturation effect (Wertz and Bolton 1972b).

The EPR intensity I corresponding to the surface under the absorption curve was calculated by numerical double integration of the EPR spectra. The uncertainty on the calculated values is about ±10%. The product IxT (with T the temperature) is proportional to the number of unpaired spins. For a normal paramagnetic species, this product does not depend on temperature. This is the case for terrestrial IOM [START_REF] Binet | Occurence of abundant diradicaloid moieties in the insoluble organic matter from the Orgueil and Murchison meteorites: a fingerprint of its extraterrestrial origin?[END_REF][START_REF] Gourier | Search for EPR markers of the history and origin of the insoluble organic matter in extraterrestrial and terrestrial rocks[END_REF]). In the synthesized IOM, IxT slightly increases between 4 K and 10 K (Fig. 3. [START_REF] Sephton | Aromatic units from the macromolecular material in meteorites: Molecular probes of cosmic environments[END_REF]. This behavior has already been observed in meteoritic IOM but also in synthetic nano-graphites (Kausteklis et al. 2011) and is probably due to a low temperature antiferromagnetic coupling between spins.

Between 10 K and 200 K, IxT is almost constant, then it slightly increases by ≈30%

between 200 K and 275 K (Fig. 3.14). This increase is however much weaker than the increase (by 150-250%) observed in meteoritic IOM and it starts at higher temperature (Binet et al, 2004) (Fig. 3.14). The behavior of the product IxT with temperature for the synthesized IOM is therefore more similar to that observed in terrestrial OM such as coals rather than in meteoritic IOM [START_REF] Binet | Occurence of abundant diradicaloid moieties in the insoluble organic matter from the Orgueil and Murchison meteorites: a fingerprint of its extraterrestrial origin?[END_REF]. Though the synthesized IOM material exhibits similar EPR parameters such as gfactor and spin concentration as the meteorite one, its variation of the EPR intensity with temperature does not reveal any significant spin pairing in the temperature range 100-300K and its behavior is closer to that of terrestrial IOM. This means that the synthesized IOM should not contain the diradicaloids which are characteristic in meteoritic IOM. However, this does not preclude their formation during further evolution of IOM either during the hydrothermal episode which may have affected on the IOM material or pressure peaks caused by mutual shocks between planetesimals or very high irradiation by Cosmic Rays as suggested in the case of carbonaceous chondrites [START_REF] Binet | Occurence of abundant diradicaloid moieties in the insoluble organic matter from the Orgueil and Murchison meteorites: a fingerprint of its extraterrestrial origin?[END_REF].

Conclusion

The chemical structure of the SOM and IOM synthesized from pentane or octane strongly supports a mechanism in which the first step is the cleavage of the hydrocarbon precursor into small (C1) species. The latter then react to form compounds with increasing number of carbon atoms. They constitute a continuum in molecular weight and are therefore distributed between soluble and insoluble fractions. This mechanism is further supported by the increase in yield when pentane is replaced by octane as precursor. However, to definitely evidence the first step of this mechanism, a synthesis was performed using CH 4 as precursor and the thus formed OM was compared to that synthesized with longer alkanes.

Chemical structure of the organic matter synthesized from methane

As reported in 3.2.1, parameters leading to the highest yields (60 min of irradiation at 60 watts forced power at room temperature, i.e. 72 °C on the vessel outer wall) were determined. These conditions were therefore used in the present synthesis with methane.

As the used amount of constantly flowing methane could not be determined due to vacuum line design, the total yield of synthesized material could not be assessed.

However, after 3 hours, only 0.13 g of OM was produced.

The synthesized sample was extracted according to the procedure described in section 2.1.2. Under these conditions, the soluble and insoluble organic matter is produced in the ratio 1:99, i.e. the synthesis was more directed toward IOM than that from octane (soluble to insoluble ratio of 15:85). Although the total yield is lower, this precursor therefore appears more efficient to synthesize IOM than longer alkanes.

Characterization of the soluble OM by GC-MS

The soluble fraction was analyzed by GC-MS (Fig. 3.15 ) and compared with that from octane (Table 3.9). All the identified compounds were present in the octanederived SOM and reciprocally. However, differences in relative abundances can be noted. Indeed, the dominant peak is pyrene whereas phenanthrene was the most abundant compound in the octane-derived SOM. Pyrene was also an important contributor to this SOM. So as to achieve a more precise comparison, the relative abundances of the SOM constituents were compared (Fig. 3.16). Whereas the 2 and 3-ring compounds are distributed on both sides of the 1:1 line, the larger compounds (4 and 5 rings) are relatively more intense when the synthesis is performed from methane. Moreover, it is interesting to note that the dominant peak in the methanederived SOM is larger (4 rings instead of 3 rings) than in the octane-derived SOM.

Taken together, these differences in distribution support a synthesis directed towards more condensed compounds as indicated by the increase in the IOM/SOM ratio when methane is used as precursor. Fig. 3.16 Relative abundances (normalized to phenanthrene) of of the SOM products synthesized from methane with respect to those from octane.

Characterization of the IOM by Py GC-MS

The synthesized IOM was analyzed using Curie point pyrolysis coupled to GC-MS (Fig. 3.17) and compared to octane-derived IOM. The signal to noise ratio of the pyrochromatogram is much lower than that of the IOM synthesized from octane although the same amount of IOM was used for pyrolysis. This can reflect a higher degree of cross-linking, hence a lower pyrolysis efficiency. This prevents any quantitative comparison with the pyrolysate of the octane-derived IOM. Nevertheless, numerous compounds could be identified in the pyrolysate of the methane-derived IOM and they appear to be similar to those identified in the pyrolysate of the octanederived IOM.

Fig. 3.17 Total ion current (TIC) of the 650°C pyrolysate of synthesized IOM from methane. Numbers refer to Table 3.10

It must be noted that the low amount of available IOM prevented from carrying out any NMR study and RuO 4 oxidation. The only information concerning the degree of aliphaticity of these compounds can therefore be derived from elemental analysis through the atomic H/C ratio. Values of 1.11 and 1.34 were obtained for the IOMs synthesized from octane and methane respectively, thus suggesting a higher aliphaticity for the latter material. However, when the aromatic moieties are compared based on the composition of the soluble fraction and of the pyrolysate, the aforementioned data highlight the similarity between the IOMs synthesized from both methane and octane. This definitely demonstrates the ability to produce IOM based on aromatic moieties in a plasma of aliphatic hydrocarbons. It therefore strongly supports the proposed mechanism for the IOM formation with the condensation of small organic radicals giving rise to aromatic units.

NanoSIMS analysis of the D enrichment in the IOM

The data from deuteriumhydrogen isotope ratio (D/H) in carbonaceous chondrites is commonly used to reconstruct the chemical processes at the origin of the hydrogen bearing compounds in the solar system. The NanoSIMS analysis of the Murchison and Orgueil IOMs revealed domains with enrichment or depletion in D compared to their bulk D/H ratio (Busemann 2006[START_REF] Remusat | Enrichment of deuterium in insoluble organic matter from primitive meteorites: A solar system origin?[END_REF]). In the frame of the comparison between the synthesized IOM and the chondritic ones, similar NanoSIMS analyses were performed on the IOMs synthesized from methane and octane. Furthermore, in the IOM produced from methane, the H/C ratio of the analyzed area is plotted versus its δD value (Fig 3.20). As the δD values changes with the H/C ratio it is considered that fractionation factors correspond to variations in the molecular structure of the IOM. These fractionation factors may originate from isotope exchange reactions such as:

H + CH x D • ⇄ [CH x+1 D] • → D + CH x+1 • (1a)
The decomposition of the complex [CH x+1 D] • is also possible via:

[CH x+1 D] • → HD + CH x • or → H 2 + CH x-1 D • (1b)
with x ranging from 0 to 2. The radicals such as C  , CH Applying an isotopic mass balance to reactions (1a) and (1b) we can write:

(D/H) CHx+1 = y  (D/H) CHx+1 + (1-y) (D/H) CHx (2)
the D/H ratio refers to the molecules designated by the subscripts,  stands for the mass independent isotopic fractionation factor and y and 1-y are the relative proportions of CH x+1 .

• and CH x • , respectively. As a result, the two parameters  and y govern the decomposition of the complex and the stabilization of the radicals under the form of IOM. Taking  =0.4 and y =0.3, we obtain δD values in reasonable agreement with the present data (Fig. 3.21).

Figure 3.21 The numerical results obtained from equation ( 2) are compared with the experimental data. The 1:1 line is drawn for reference. The black dots correspond to  = 0.4 and y = 0.3. The precision on the calculated δD values was calculated from ±0.05 random variations on  and y. The precision on the measured δD values is ±100‰ i.e. the width of the step used to construct the distribution function f(δD) reported in Figure 3.20.

Discussion and comparison with meteoritic IOM

The purpose of the present work was to test the ability of synthesizing macromolecular material from small aliphatic units under presolar disk conditions corresponding to regions where a massive (photo)dissociation of gaseous molecules took place. However, it must be noted that we do not address the physical cause of the dissociation (dense UV photon-dominated regions, high velocity shocks, …)

As the present synthesis only involves C and H atoms and no heteroelement whereas the latter substantially contribute to the meteorite IOM, the comparison between the presently synthesized materials and the meteorite IOM should be limited to its hydrocarbon skeleton. Both materials exhibit an aromatic character with a chemical structure based on small aromatic units, as directly imaged by HRTEM for the IOM synthesized from octane. Indeed the average length of the aromatic layers in the disordered area of the synthesized material (0.48 nm) is comparable to that previously reported for Murchison and Orgueil IOM (0.55-0.58 nm; [START_REF] Derenne | Size discontinuity between interstellar and chondritic aromatic structures: A high-resolution transmission electron microscopy study[END_REF]. In both cases, the more frequent structure corresponds to about a length of 2 fused rings (layers of about 4 fused rings if the structure is considered as isometric).

Moreover, these values contain important information: (i) the synthesized IOM is not amorphous (i.e. made of randomly distributed carbon atoms) since sub-nanometric fringes are detected and (ii) this synthesized carbonaceous matter is very far from graphite for which graphene layer size is more than 100 nm and such layers are stacked by tens (whereas sub-nanometric layers of the synthesized IOM are often single, or piled by two units). Finally, in chondrites of petrologic type >3.0, the evolution of the IOM is controlled by the extent of thermal metamorphism. The polyaromatic layers, shorter than 1 nm in petrologic type ≤ 3.0 chondrites, grow up to sizes between 5 and 10 nm in petrologic type >3.6 chondrites, contributing to the increase of the degree of structural order (Le [START_REF] Guillou | High resolution TEM of chondritic carbonaceous matter: Metamorphic evolution and heterogeneity[END_REF]. Therefore, according to HRTEM, the synthesized IOM appears to be very similar to the pristine meteoritic IOM as found in non-thermally metamorphosed meteorites.

Beside these aromatic units, FTIR and solid state 13 C NMR revealed the presence of aliphatic carbons. Using variable contact time experiment in the CP/MAS sequence, a comparison between the relative abundance of aliphatic and aromatic carbons in the meteorite and synthesized IOM can be achieved although it must be restricted to the carbons which do not bear any heteroelement. Quantitative data derived from NMR have been published on a relatively restricted set of carbonaceous chondrites, namely Murchison, Orgueil, EET92042 and Tagish Lake [START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF][START_REF] Cody | NMR studies of chemical structural variation of insoluble organic matter from different carbonaceous chondrite groups[END_REF][START_REF] Cody | Solid-state (1H and 13C) nuclear magnetic resonance spectroscopy of insoluble organic residue in the Murchison meteorite: a self-consistent quantitative analysis[END_REF]. They reveal differences in aromaticity, (i.e. the intensity ratio of aromatic to total signal) with the following order of increasing aromaticity, from EET92042 to Orgueil, Murchison and Tagish Lake.

This has been interpreted as the result of a progressive trend of IOM alteration on the parent body, the aromatic units being considered as more refractory than the aliphatic chains. The presently synthesized IOM exhibits a higher aliphatic character than Orgueil, Murchison and Tagish Lake and rather similar to that of EET92042. This is further supported by an H/C elemental ratio of 1.11 for the synthesized IOM from octane (that from methane being even more aliphatic with a H/C ratio of 1.34), substantially higher than that of the IOM from Orgueil, Murchison and Tagish Lake.

As far as we are aware, RuO 4 oxidation was only performed on Orgueil and Murchison meteorites (Remusat et al. 2005a). They mainly released aliphatic di-and tricarboxylic acids, along with benzenecarboxylic acids although in lesser amount.

These products are also identified in the present study (Tables 3.7 and3 (Remusat et al. 2005a). Numbers refer to Table 3.7 and isomers of 18 have been distinguished for a better comparison with meteorite data.

A more precise comparison between meteorite and synthesized IOM can be achieved through Py-GC-MS and RuO 4 oxidation. Indeed, molecular information can be derived from these techniques on aromatic and aliphatic units, respectively. Most of the compounds identified in the pyrolysate of the synthesized material were also reported upon pyrolysis of Murchison and Orgueil (Table 3.3). Moreover, to achieve quantitative comparison between the extraterrestrial and synthesized samples, the relative abundances were compared. To this end, the peak intensities were normalized to 2-methylnaphthalene, as this compound is the most abundant one in the present pyrolysate, and further compared with those calculated from Murchison and Orgueil pyrolysate (Fig. 3.23) A general good agreement is observed as most compounds fall close to the 1:1 line, especially when compared with Orgueil. The relative abundance of the diacids increases from C 4 to C 6 and then decreases in the synthesized IOM whereas a regular decrease with the chain length is observed in the meteorites. It must also be noted that the methyl substituted diacids are more abundant than their parent compound (e.g. 17 and 18 with respect to 16) contrary to what was observed in Orgueil and Murchison. Another major difference between these two types of IOM is the presence of the C 5 to C 10 monocarboxylic acids (Fig. 3.11, Table 3.7) which were not observed in the meteorites.

Taken together, the differences in distribution and the presence of monocarboxylic acids are consistent with the higher aliphaticity previously deduced from NMR for the synthesized IOM. The presence of ketoacids and cycloalkanoic acids in the RuO 4 oxidation products and of non-aromatic cyclic products in the pyrolysate of the IOM suggests a substantial contribution of non-aromatic unsaturated and saturated rings in the chemical structure of the synthesized IOM.

The latter were at most present in much lower abundance in the meteorites. As these structures can be considered as intermediates in the aromatization process, it seems that the synthesized IOM has not reached the same aromatization stage as the one observed in Orgueil and Murchison IOM. Two hypotheses can be put forward to account for this difference. (i) Either all the aforementioned meteorites share a common precursor and they further undergo aromatization to different extents, EET92042 being the most pristine; (ii) or they are formed in different regions of the nebula where slightly different conditions prevail especially for dissociation rates and therefore hydrogen content. This second hypothesis is supported by a recent study reporting on the influence of plasma temperature on its composition [START_REF] Lombardi | Study of an H 2 /CH 4 moderate pressure microwave plasma used for diamond deposition: modelling and[END_REF]. In this study, the distribution of the various species in a CH 4 /H 2 microwave discharge is determined as a function of temperature, thus showing that the higher plasma temperature, the more atomic hydrogen. Atomic hydrogen being known to prevent the formation of aromatic hydrocarbons, less aromatic material will be formed under conditions that favor high plasma temperature. In this context, EET92042 would be formed in nebula regions where higher dissociation rates take place whereas the more aromatic Tagish Lake would have formed in regions with lower dissociation rates, the synthesis performed in the present study being more representative of the formation of IOM from EET92042.

Synthesis and analysis of organic matter containing nitrogen

Introduction

Among heteroelements, although less abundant than oxygen, nitrogen substantially contributes to the IOM isolated from carbonaceous chondrites with N/C ratios ranging from 0.012 [START_REF] Zinner | Meteorites and the Early Solar System Univ[END_REF]) to 0.044 [START_REF] Pearson | Intra-and intermeteorite heterogeneity in carbon and nitrogen abundance and isotopic compositions within CM chondrites 31st Lunar and Planetary Science Conference[END_REF]. This element more specifically gave rise to the interest of scientists due to the presence of amino acids in the soluble OM from meteorites [START_REF] Cronin | Organic matter in carbonaceous chondrites, planetary satellites, asteroids and comets[END_REF] and numerous studies are still performed to ascertain the origin of these molecules [START_REF] Elsila | Compound-specific carbon, nitrogen, and hydrogen isotopic ratios for amino acids in CM and CR chondrites and their use in evaluating potential formation pathways[END_REF]. Whereas a large diversity of chemical structures was reported for the nitrogen-containing products in the SOM [START_REF] Sephton | Multiple Cosmic Sources for Meteorite Macromolecules?[END_REF], less is known about its occurrence within the IOM. Pyrolysis was first used to release N-containing products but the latter are often scarce in pyrolysates. The most commonly detected pyrolysis product is benzonitrile along with acetonitrile [START_REF] Levy | The organic analysis of the murchison meteorite[END_REF][START_REF] Holzer | The organic composition of the Allan Hills carbonaceous chondrite (77306) as determined by pyrolysis-gas chromatography-mass spectrometry and other methods[END_REF], Remusat et al. 2005b) suggesting the presence of cyano groups in the chemical structure although the location of nitrogen within heterocyclic units was also put forward. Indeed, Murchison IOM pyrolysis also led to the tentative identifications of the cyanuric acid [START_REF] Studier | Origin of organic matter in early solar system-V. Further studies of meteoritic hydrocarbons and a discussion of their origin[END_REF],and alkyl pyridines [START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF] while substituted pyridine, quinoline, and carbazole were released upon its sodium dichromate oxidation [START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF] or hydropyrolysis [START_REF] Sephton | Organic matter in ancient meteorites[END_REF]). Solid state 15 N NMR of Orgueil IOM demonstrated that nitrogen was mainly located within pyrrole moieties although a small contribution of nitrile groups was considered with a pyrrole to nitrile ratio of ca. 5 (Remusat et al. 2005b). Furthermore no other nitrogen containing compounds such as amide or amine could be detected from this analysis.

Despite this information about nitrogen speciation in the IOM, its origin is still poorly understood. Large 15 N anomalies were observed in organic globules in meteorites [START_REF] Messenger | Identification of molecular-cloud material in interplanetary dust particles[END_REF] and they were interpreted as possible contributions from cold molecular clouds and the outer protosolar disk where organic ice coatings on grains could be photochemically processed into refractory organic matter (Nakamura- [START_REF] Nakamura-Messenger | Organic Globules in the Tagish Lake Meteorite: Remnants of the Protosolar Disk[END_REF]). However, the chemical nature of the precursor of nitrogen is still debated. Indeed, N 2 has been for long considered as the main form of nitrogen in the interstellar medium but it is now more commonly considered that N is mostly atomic and ammonia is preferred as the main source of N in OM. Indeed, as detailed below, recent observations of several nitrogen-bearing species in the interstellar medium led to possible mechanisms and these may explain presence of nitrogen in meteorite IOM. In general, molecular clouds are the reservoir of the nitrogen which is expected to be gaseous. In these regions either atomic or molecular forms of nitrogen are considered. Thus several key reactions involved in the chemistry of interstellar nitrogen were established (Fig. The aim of the present chapter was to test two potential precursors of N in the IOM, following the same rationale as used in the previous chapters. To this end, two types of syntheses were performed in organic plasmas thanks to the device previously used to build up the hydrocarbon skeleton of the IOM. The first one involved hexylamine as a precursor of nitrogen hydrides and in the second one, octane was irradiated in the presence of N 2 .

4.2 Synthesis in the presence of nitrogen hydrides

Synthesis

The previously defined parameters leading to the highest yields (60 min of irradiation at 60 watts forced power at room temperature) for the OM synthesis from octane were used in the present experiment performed with either pure hexylamine or a mixture of hexylamine and octane (1:1, v:v). This mixture was used to decrease the N/C ratio in the precursor (from 0.17 to 0.07) so as to get closer to the low IOM N/C values (0.02-0.03). The minimum total yield of synthesized materials from hexylamine and mixture of hexylamine and octane was 31% and 32%, respectively.

This yield was calculated as previously.

The synthesized sample was extracted according to the procedure described in the previous chapter and as reported by [START_REF] Biron | Toward an experimental synthesis of the chondritic insoluble organic matter[END_REF]. Under these conditions, the soluble and insoluble organic matter are produced in 12:88 and 16:84 ratios from pure hexylamine and hexylamine/octane mixture, respectively.

The presence of nitrogen seems to enhance the synthesis as the yield is about twice that obtained with octane only (15 %) but without favoring the formation of IOM as the soluble to insoluble ratio remains close to that previously reported for octane (15:85).

Characterization of the soluble OM by GC-MS

GC-MS traces of the SOM synthesized during irradiation of pure hexylamine and of hexylamine/octane mixture are both dominated by polycyclic hydrocarbons and methylated homologues that were previously reported in the synthesis performed with octane [START_REF] Biron | Toward an experimental synthesis of the chondritic insoluble organic matter[END_REF]. However, several nitrogen-containing compounds also contribute to the GC-MS traces, nitrogen occurring either as cyano substituents of aromatic compounds (5,8,9,[START_REF] Sephton | Aromatic units from the macromolecular material in meteorites: Molecular probes of cosmic environments[END_REF]15,18,20,23,27,31) or within the heterocycle, aromatic (22,26) or not (2, 7). The aromatic compounds substituted by cyano groups are benzene, toluene, naphthalene, fluorene and anthracene which were formed in the synthesis using hydrocarbon precursor. They reflect the addition of a C≡N group likely resulting from dehydrogenation of °CH 2 -NH 2 radicals onto aromatic moieties formed upon irradiation. Naphthalenecarbonitriles ( 14) are the most abundant Ncontaining compounds. Incorporation of N as heterocycle mainly leads to pyridine moieties that may occur within quinoline or acridine units although two methylpiperidine derivatives (2 and 7) were also identified when pure hexylamine is used as precursor. The latter results from the direct cyclisation of the hexylamine itself and it can be assumed that at least a part of the pyridine units were formed through further aromatization of the piperidine rings. In addition, the unreacted compound is detected in the SOM reflecting uncomplete cleavage into radicals upon irradiation.

Moreover, the intensity of the compounds eluting at the beginning of the trace of the SOM synthesized from octane/hexylamine mixture is rather lower than that obtained from pure hexylamine. This difference reflects the solubility of the lightest compounds in unreacted octane. Moreover, when hexylamine is used as the sole precursor, the number of the Ncontaining compounds increase (likely due to detection threshold) as well as their 123 relative abundances, thus reflecting the higher N content in the reagent. This can be illustrated by the comparison of the relative abundances of these compounds in the two traces (Fig. 4.3).

Characterization of the IOM

Elemental analysis of the synthesized IOMs revealed N contents of 6.6 and 7.2 % leading to N/C atomic ratios of 0.07 and 0.08, evidencing nitrogen incorporation during the synthesis. As expected, a slightly higher incorporation is obtained with pure hexylamine.

The insoluble organic materials were analyzed using solid state 13 C NMR spectroscopy. Solid state 13 C NMR spectra of the IOM synthesized from pure hexylamine and hexylamine/octane mixture comprise two dominant peaks which are attributed to aliphatic and aromatic carbons (Fig. 4.5) as previously observed when synthesis was performed from octane [START_REF] Biron | Toward an experimental synthesis of the chondritic insoluble organic matter[END_REF]. The peak at 0-60 ppm assigned to carbon in aliphatic chains maximizes at 35 ppm (C in aliphatic chains)

and it shows two shoulders at 14 ppm and 21 ppm which reveal the presence of methyl groups linked to aliphatics and aromatics respectively. The decomposition of the spectra ( assigned to C≡N stretching vibration thus revealing the presence of the cyano group that could not be evidenced from the NMR spectra. Indeed, C in cyano groups resonate around 120 ppm and thus were masked by the prominent peak at 127 ppm due to non-protonated aromatic carbons. It must be noted that 2217 cm -1 band appears to be more intense when pure hexylamine is used when compared with the hexylamine/octane mixture and that it was lacking on the spectrum of the IOM synthesized from octane. Finally, a broad band at 3370 cm -1 can be assigned to N-H groups. In addition, nitrogen-containing compounds could be identified. Nitrogen occurs either as heteroelement within pyrrole (6, 9, 14) or pyridine ring, the latter occurring as such (30) or within a quinoline moiety (24, 42), or as cyano groups substituting aromatic compounds such as benzene (13,17) or naphthalene (32, 37).

Hexanenitrile ( 4) is also identified in the pyrolysate, it is the direct dehydrogenation product of hexylamine. Taken together, these pyrolysis products exhibit some similarities with the compounds identified in the soluble fraction, thus supporting the idea that the main difference between the two fractions is the molecular weight, i.e. the polymerization stage. However, some differences can be highlighted such as the lack of pyrrole or the presence of piperidine rings in the soluble fraction, which may reflect side reactions taking place upon pyrolysis. As expected the most abundant and diverse nitrogen compounds are detected in the IOM made from hexylamine alone, as illustrated by the comparison of relative abundances of N-compounds occurring in both IOMs normalized to pyrene (Fig. 4.9).

Synthesis

The synthesis with octane and N 2 was carried out with the optimal conditions (60 min of irradiation at 60 watts forced power at room temperature). The minimum total yield of synthesized material was 9%. As the used amount of constantly flowing nitrogen could not be determined due to vacuum line design, this yield is calculated with respect to the used amount of octane. The presence of flowing nitrogen seems to inhibit the synthesis as the yield is nearly two times lower than that obtained with pure octane (15 %).

The synthesized sample was extracted according to the procedure described in the previous chapter and as reported by [START_REF] Biron | Toward an experimental synthesis of the chondritic insoluble organic matter[END_REF]. Under these conditions, the soluble and insoluble organic matter are produced in 19/81 ratio.

Characterization of the SOM by GC-MS

As in the previous syntheses, the GC-MS analysis of SOM revealed numerous polycyclic hydrocarbons with two (1-4) to five rings (24, 25) (Fig. 4.10, Table 4.3).

These hydrocarbons were previously identified in the SOM produced from irradiated octane and their relative abundances were compared (Fig. 4.11). No clear trend with the number of rings could be derived from this comparison with cyclopentaphenanthrene (17), fluoranthene (19) and pyrene (20) being more abundant in the SOM produced from octane and N 2 but acenaphthylene (5) and methylfluorenes (11) contributing less to this SOM. Moreover, the irradiation of octane and molecular nitrogen produced only two isomers of one compound in the soluble fraction, namely naphthalenecarbonitriles (7).

Characterization of the IOM

The elemental analysis of the IOM synthesized from octane in the presence of N 2 shows a rather low incorporation of nitrogen with a N content of 1.8 % and a N/C atomic ratio of 0.02. So as to compare with previously described IOMs, the synthesized IOM from irradiated octane and nitrogen was analyzed by solid state 13 C NMR. The spectrum is comparable to that obtained from octane alone as it comprises two main peaks which are attributed to aliphatic and aromatic carbons (Fig. 4.12). The most abundant peak with max at 35 ppm corresponds to aliphatic carbons. It shows two shoulders at 13 and 21 ppm previously assigned to methyl groups linked to aliphatic and aromatic C, respectively. Its decomposition (Fig. 4.12b) requires a peak at 58 ppm which was not present in the IOM synthesized from octane and thus shall reflect the presence of aliphatic carbons linked to nitrogen. The peak corresponding to aromatics shows contributions from protonated (126 ppm) and nonprotonated (138 ppm) carbons as in the IOM derived from octane. However, an additional small signal at 162 ppm is observed and it was assigned to sp 2 C in heterocycles. It must be noted that no signal from cyano groups can be evidenced from the NMR spectrum as its resonance (ca. 120 ppm) falls below the nonprotonated aromatic C peak. The FTIR analysis confirmed the previous findings. Indeed, the comparison of the spectra of IOM synthesized from octane in the presence or not of nitrogen (Fig. 4.13) reveals some small differences. We can notice the appearance of a broad band maximizing at 3370 cm -1 , assigned to N-H groups, and of one at 2217 cm -1 indicating the presence of C ≡ N stretching absorption. Naphthalenecarbonitrile was also identified in the SOM fraction (see 4.3.2). The presence of this compound indicates some N incorporation in the IOM in agreement with elemental analysis. However, the low abundance of this sole N-containing compound shows that this incorporation is quite limited. No aliphatic compound could be detected using selective ion detection at m/z 57 except unreacted octane (2).

Comparison with chondritic IOM

Elemental analysis of IOMs isolated from carbonaceous chondrites revealed the contribution of nitrogen among the heteroatoms. Spectroscopic investigations along with thermal and chemical degradation suggest that this nitrogen mainly occurs within heterocyclic moieties as well as, although to a lesser extent, in cyano groups.

The purpose of this work was to test whether nitrogen could be incorporated into the macromolecular material under presolar disk conditions where photo dissociation of gaseous molecules takes place and if yes, what is its chemical speciation. To this end, the same device as previously used to build up the hydrocarbonaceous backbone of the IOM was used. Two types of nitrogen precursors were tested:

nitrogen hydrides, formed in situ upon microwave discharge of an aliphatic amine (hexylamine) and molecular nitrogen N 2 . In both cases, N is incorporated within the IOM, the hexylamine precursor leading to a higher N content in the IOM than N 2 .

However, the comparison with the IOM synthesized from pure octane shows that this incorporation does not significantly affect the hydrocarbonaceous backbone. NMR spectroscopy along with FTIR, point to the presence of heterocycles and cyano groups. This is supported by the identification of the SOM constituents and of the IOM pyrolysis products in the case of the irradiation of hexylamine but not in the case of irradiation of octane in the presence of N 2 as only naphthalenecarbonitriles and methylbenzonitrile could be detected . This should reflect differences in nitrogen speciation between these two IOMs due to differences in the nitrogen precursor although this is not clearly evidenced by the spectroscopic data. As a lower N incorporation took place with octane and N 2 when compared to hexylamine, this difference may also be due to detection threshold, especially as naphthalenecarbonitriles are also the main N-constituents of the SOM in the hexylamine experiment and naphthalenecarbonitriles and methylbenzonitriles in IOM.

However, the relative abundance of the other N-containing compounds in this fraction would make their detection possible in the case of the synthesis performed with octane and N 2 .

The most commonly reported N-containing pyrolysis product, benzonitrile (Remusat et al. 2005b) is not detected in the present pyrolysates. However, methylbenzonitriles and ethylbenzonitrile are identified in the case of hexylamine pointing to some similarity. Moreover, substituted pyridine and quinoline moieties previously reported in meteorite IOM [START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF] were also identified in the pyrolysis products of this synthesized IOM. Finally, it must be noted that acetonitrile was reported by Levy [START_REF] Levy | The organic analysis of the murchison meteorite[END_REF]) in Murchison but it cannot be detected in the present experimental conditions due to its small molecular weight and so low boiling point.

Despite these differences, the laboratory synthesized organic matter from hexylamine, i.e. nitrogen hydrides, exhibit many similarities with the IOM isolated from Murchison or Orgueil. O 2 fugacity and water/rock ratio) [START_REF] Zolensky | Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites[END_REF].

The aim of the present study was to experimentally investigate the two aforementioned potential pathways of O incorporation in the chondritic IOM. To this end, two experimental approaches have been designed:

(i) In the previous chapter, IOM synthesized from hydrocarbonaceous small radicals was shown to reproduce key features of the chondritic IOM. We therefore used this synthetic IOM as a model material to investigate the behavior of chondritic IOM when submitted to aqueous alteration. To this end, the synthetic IOM was refluxed in water for 6 months. The released soluble compounds were analyzed as well as the left-over IOM.

(ii) To test whether O can be incorporated within the macromolecular network upon its formation, a synthesis was performed under similar conditions as those described in the preceding chapter but involving some hydroxyl radicals in addition to the CH x ones. Ethanol was used as the source of hydroxyl radicals because of its miscibility with octane.

Simulation experiment for aqueous alteration

Experimental

25 mg of IOM previously synthesized from octane was refluxed for 6 months in 5 ml of distilled water. The IOM was separated from the water by filtration onto glass fritted funnel. The aqueous supernatant was extracted with MeOH : DCM mixture (1:1 v:v) to recover organic compounds potentially released upon water reflux. This organic extract was analyzed by GC-MS after silylation. The introduction of BSTFA allows replacement of protons in OH groups with trimethylsilyl groups making the derivatives suitable for GC analysis and as a result, it permits detection of polar compounds such as alcohols or carboxylic acids.

The dried IOM was analyzed with elemental analysis, FTIR and Py GC-MS techniques. So as to highlight the presence of polar moieties within the IOM, pyrolysis was performed in the presence of a derivatization reagent (tetramethylammonium hydroxide TMAH) which allows the methylation of the pyrolysis products [START_REF] Challinor | The development and applications of thermally assisted hydrolysis and methylation reactions[END_REF].

Released soluble compounds

The soluble organic compounds released upon water refluxing were analyzed by GC-MS after silylation. These compounds can be a priori considered as alteration products of the IOM. Aromatic hydrocarbons and oxygenated polycyclic compounds can be identified in addition to a series of C 8 to C 18 fatty acids (Table 5.1). So as to rule out any potential contamination during this simulation experiment, a preliminary experiment was carried out using labelled IOM. To this end, IOM synthesized from 99.5% deuterated pentane was refluxed in water and analyzed by GC-MS (Fig. 5.1). 5.2; Table 5.1). Their presence in the organic extract of the aqueous phase of the refluxed IOM therefore suggests that they were occluded in the IOM macromolecular network. This is further supported by their release in the 358°C pyrolysate of the IOM (see section 3.2.5). All the other compounds released from IOM upon water reflux contain oxygen functions (keto or acid group) and a polycyclic and/or aromatic skeleton except the butanedioic acid (5). This short diacid was previously released in the RuO 4 oxidation of the synthesized IOM and also of the chondritic one. It is considered to be derived from the short aliphatic linkages between the aromatic moieties of the macromolecule. The other compounds comprise one to four rings, the benzoic acid (3) being the most abundant. This compound was also produced upon RuO 4 oxidation of the synthesized and chondritic IOMs. Its methylated homologues (7 and 10) also contribute to the extract, in agreement with the substitution of the aromatic rings in the IOM inferred from its pyrolysis products which comprise C1-to C3-alkylbenzenes [START_REF] Biron | Toward an experimental synthesis of the chondritic insoluble organic matter[END_REF]. The benzene dicarboxylic acid (12) also contributed to the RuO 4 oxidation products of the synthesized and chondritic IOMs. It reflects the oxidation of disubstituted benzene rings. The two-ring compounds are methylnaphthylketone (11) and naphthalene carboxylic acid [START_REF] Sephton | Aromatic units from the macromolecular material in meteorites: Molecular probes of cosmic environments[END_REF] which are the higher homologue of acetophenone and benzoic acid, respectively. They reflect the alteration of the naphthalene moieties of the IOM. Similarly, the indanone is the modified derivative from indene or indane, which were previously identified in the IOM obtained from octane. The latter were shown to be abundant based on the distribution of the pyrolysis products [START_REF] Biron | Toward an experimental synthesis of the chondritic insoluble organic matter[END_REF]. Finally, three-and four-ring compounds bearing a keto group are identified. They are fluorenone (13), anthrone It is interesting to note that fluorenone (13) was reported as one of the most abundant compound of the extract of Murchison meteorite [START_REF] Huang | Hydrogen and carbon isotopic ratios of polycyclic aromatic compounds in two CM2 carbonaceous chondrites and implications for prebiotic organic synthesis[END_REF]. In this extract, these authors also identified the two isomers of methylnaphthylketone ( 11)

along with anthrone (16). Moreover, Peltzer [START_REF] Peltzer | The chemical conditions on the parent body of the murchison meteorite: Some conclusions based on amino, hydroxy and dicarboxylic acids[END_REF]) and Cronin [START_REF] Cronin | Organic Matter in Meteorites: Molecular and Isotopic Analyses of the Murchison Meteorite[END_REF] identified a large suite of aliphatic dicarboxylic acids water refluxed extract of Murchison among which butanedioic (5) and isomers of pentanedioic (6, 9)

were the most abundant. These authors also identified a series of αhydroxycarboxylic acids comprising hydroxypropanoic acid (1) as the main constituent. Finally benzoic acid (3) and its methylated homologue (7) were identified in hot water extracts of Murchison (Huang et al., 2005). The occurrence of similar compounds in meteorite extracts and in the synthesized IOM hot water extracts further validates the use of the synthesized IOM as a model for the chondritic IOM backbone. Moreover, it supports the origin of these compounds as hydrothermal alteration products of the meteorites.

IOM analysis

So as to reveal potential oxygen incorporation in the chemical structure of the IOM, the left-over IOM was analyzed through elemental analysis, FTIR and pyrolysis coupled to GC-MS. It must be noted that no NMR could be performed due to the too low amount of available material. stretching vibration at 3417 cm -1 , C=O stretching at 1695 cm -1 and C-O stretching at 1230 cm -1 and 1100cm -1 . The 1695 cm -1 band overprints a previously existing weak band at 1680 cm -1 , which was attributed to C=C stretching in cycloalkenes. It must be noted that the signature of the aliphatic C-H groups between 2800 cm -1 and 3000 cm - 1 , the bands at 1450 cm -1 and 1375 cm -1 corresponding to -CH bending and the aromatic C=C band at 1600 cm -1 are preserved in the refluxed sample.

Taken together, the above FTIR features of the refluxed IOM clearly demonstrate an alteration of the chemical structure of the starting IOM with oxygen incorporation within hydroxyl and carbonyl groups.

Pyrolysis-GC-MS analysis of the IOM

So as to get insight in the chemical structure at the molecular level, pyrolysis coupled with GC-MS was used (Fig. 5.4). However, as stressed above, when aiming at detecting polar moieties, pyrolysis must be performed in the presence of a derivatization reagent. This was achieved using tetramethylammonium hydroxide (TMAH) which provides in situ methylation, as well as thermally assisted base hydrolysis.

* -compounds derived from TMAH Fig. 5.4 Total ion current (TIC) of the TMAH pyrochromatogram of refluxed IOM. Numbers refer to Table 5.2

Most of the products identified in the thermochemolysate of the refluxed IOM (Table 5.2) are identical to the pyrolysis products of the starting IOM (Remusat et al. 2005b). They mainly correspond to aromatic and polycyclic hydrocarbons. However, a few oxygen-containing compounds are also detected in this thermochemolysate.

Although their intensities are very low when compared to those of the aromatic hydrocarbons, they reveal some alteration of the chemical structure of the IOM.

Benzoic acid (9) (occurring as its methyl ester due to in situ derivatization with TMAH) is the most abundant of the oxygen-containing pyrolysis products and it reveals the oxidation of the aromatic rings which build up the macromolecular network of the IOM. An aromatic ketone, acetophenone ( 8) is also identified. It reveals the oxidation of the aliphatic linkages between the aromatic units and it must be noted that it may be intermediates toward the formation of benzoic acid. A phenolic compound (10) (present as its methylated ether because of TMAH) also contributes to this pyrolysate. All these compounds bear an aromatic ring and can thus be directly related to the chemical structure of the starting IOM. Although less visible than through the formation of the soluble compounds, the alteration of the macromolecular network is therefore evidenced through the analysis (FTIR and pyrolysis) of the IOM. Benzoic acid ( 9) was identified as one of the most abundant oxygenated product in the thermochemolysate of both Orgueil and Murchison IOM (Remusat et al. 2005a, Watson, Sephton and[START_REF] Watson | Thermochemolysis of the Murchison meteorite: identification of oxygen bound and occluded units in the organic macromolecule[END_REF]. Moreover acetophenone (8) itself was present in very low amount in both pyrolysates. Finally the dimethyl phenol was identified in the pyrolysate of Orgueil IOM which corresponds to dimethylanisole (10) in the presently analyzed product due to the presence of TAMH upon pyrolysis. From the present results, it can thus be anticipated that these compounds reflect at least partly the hydrous alteration of the macromolecular network.

Incorporation of Oxygen upon IOM formation

Synthesis

Synthesis was performed using the optimal conditions reported by Biron [START_REF] Biron | Toward an experimental synthesis of the chondritic insoluble organic matter[END_REF]for the IOM synthesis from octane, i.e. 60 min of irradiation at 60 watts forced power at 72 °C. The aim of this synthesis was to test the reactivity of hydroxyl groups in the hydrocarbon plasma. To this end, ethanol was used as a precursor of these groups and mixed with octane. The selection of this specific alcohol was based on its miscibility with octane. In order to achieve an homogeneous mixture, the two reagents were mixed prior to the irradiation experiment. The volume proportion 1:4 for octane: ethanol was chosen to give as close as possible O/C ratio (0.25 in the precursor mixture) as that of meteorites (≈ 0.2).

The total minimal yield of synthesized material is 35% and is calculated by division of the final mass of the product by initial masses of both totally consumed reagents multiplied by 100. Soluble and insoluble organic matter were separated after solvent extraction and they are produced in the ratio 17:83. This value is rather close to the value obtained from octane alone (15:85; [START_REF] Biron | Toward an experimental synthesis of the chondritic insoluble organic matter[END_REF]).

Characterization of the soluble OM by GC-MS

Soluble organic matter extracted from synthesized OM was analyzed with GC-MS (Fig. 5.5). All but one of the identified compounds were hydrocarbons (Table 5.3). So as to reveal potential oxygencontaining compounds which would not be GCamenable, the SOM was silylated prior to the injection. Nevertheless no additional peak could be detected. The soluble organic matter synthesized from the mixture of octane and ethanol consists of number of aromatic compounds ranging from three (1-6) to five rings (13-21), the most abundant being pyrene (10) and cyclopentaphenanthrene (7). These compounds were previously identified in the SOM obtained from octane alone except the heaviest ones (18-21). In the same way, the lightest compounds that were identified in the SOM obtained from octane (naphthalene, methylnaphthalenes, C2alkyl and C3-alkylnaphthalenes, biphenyl, biphenylene and acenaphthylene) could not be detected in the SOM synthesized from the mixture of octane and ethanol.

Moreover, the phenalene (1) is only present in trace amounts whereas it was a substantial contributor to the SOM synthesized from octane and the relative abundance of phenanthrene (3), which was the most abundant product in SOM from octane, is strongly reduced (the peak intensity of phenanthrene (3) to pyrene (10) decreased from 1.06 to 0.43). This difference likely reflects the high solubility of these compounds in ethanol. Indeed, naphthalene is much more soluble in ethanol (179 g/100 g at 70°C) than in alkane (78.8 g/100 g at 70°C in hexane). Thus it is anticipated that during the irradiation experiment, as soon as these compounds formed, they were dissolved in partially undissociated ethanol and directly pumped out the vacuum line. Although it is likely that additional oxygen-containing compounds were also formed and lost through the same pathway, one could be identifiedbenzoanthracenone (17), aromatic ketone which is associated to its hydrocarbonaceous compound benzoanthracene also detected in the analyzed matter.

Analysis of IOM

Although SOM analysis only pointed to limited oxygen incorporation upon irradiation of octane/ethanol mixture, elemental analysis led to O/C ratio of 0.08. Moreover, the chemical functions of the IOM were thus investigated through FTIR and solid state 13 C NMR.

The FTIR spectra of IOM samples synthesized from octane alone and mixture of octane and ethanol are compared (Fig. 5.6). The spectrum of the IOM obtained from octane and ethanol exhibits a broad band at 3370 cm -1 due to OH stretching vibrations and a shoulder at 1720 cm -1 of the 1615 cm -1 band, which can be assigned to C=O stretching vibrations in acids or ketones. These features reveal O incorporation in the macromolecular network of the IOM. It must be noted that the bands around 2900 cm -1 (aliphatic C-H stretching absorptions) and at 1450 and 1375 cm -1 (asymmetrical CH 2 and CH 3 and symmetrical CH 3 bending vibrations, respectively) are common features of both spectra. The IOM produced from a mixture of n-octane and ethanol (v:v 1:4) was analyzed using pyrolysis GC-MS. TMAH thermochemolysis was also performed to highlight the polar moieties of the IOM. However, the comparison of the two traces did not afford any difference and the TMAH thermochemolysis trace is not shown. The pyrolysate (Fig. 5.8 Table 5.4) contains a large number of compounds which mainly are aromatic hydrocarbons. The most abundant compounds are toluene (1) and acenaphthene (23). Most of the products identified in the pyrolysate are similar to those obtained from octane (Table 3.3). The main difference relies on a few oxygencontaining compounds which are detected in the IOM synthesized from octane and ethanol, although their abundance is considerably lower than that of the aromatic hydrocarbons. They are alcohols such as tetrahydronaphthol (13) which reflects hydroxyl addition to naphthalene moieties, the latter being predominant in the IOM as

shown by the abundance of naphthalene ( 14) and methylated homologues (18, 19, 21, 24) in the IOM pyrolysate (section 3.2.4). Similarly, biphenylmethanol (25) can also be related to the biphenyl structures revealed by the pyrolysis products ( 20) and ( 28). Although in trace amounts, the oxygen-containing pyrolysis products reflect the incorporation of oxygen in the macromolecular network of the IOM. However, as far as we are aware, none of these compounds was reported in the pyrolysate/thermochomolysate of chondritic IOM making this formation pathway more unlikely.

Comparison with chondritic IOM

Beside carbon and hydrogen, oxygen is the most abundant element in the IOM. The analysis of the IOM isolated from Murchison and Orgueil meteorites reveals several forms of oxygen-containing functional groups. C-XANES [START_REF] Wirick | Organics in the Murchison meteorite using carbon XANES spectroscopy[END_REF]) and 13 C NMR [START_REF] Cody | Solid-state (1H and 13C) nuclear magnetic resonance spectroscopy of insoluble organic residue in the Murchison meteorite: a self-consistent quantitative analysis[END_REF][START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF] spectra showed the presence of carboxyl and carbonyl groups (absorption at 288.9 eV and resonance at 200 and 168 ppm) and aliphatic alcohols or ethers at 55 ppm. Furthermore, the presence of oxygen-containing compounds was supported by pyrolysis/ thermochemolysis where phenols and aromatic ketones are identified along with benzoic acid (Remusat et al. 2005b[START_REF] Studier | Origin of organic matter in early solar system-V. Further studies of meteoritic hydrocarbons and a discussion of their origin[END_REF][START_REF] Watson | Thermochemolysis of the Murchison meteorite: identification of oxygen bound and occluded units in the organic macromolecule[END_REF]. Hydrous pyrolysis as well as oxidation using several reagents released oxygenated products from chondritic IOM [START_REF] Hayatsu | Origin of organic matter in the early solar system-VII. The organic polymer in carbonaceous chondrites[END_REF], Yabuta et al. 2007) but the oxygen atoms likely originate at least partly from the reagent making these techniques unsuitable for oxygen function investigation.

In the present study, two types of experiments were performed to investigate the potential source of oxygen in the chondritic IOM. They were designed to address the two main scenarios proposed in the literature: aqueous alteration in the asteroidal parent body [START_REF] Zolensky | Meteorites and the early solar system[END_REF] or oxygen incorporation by reactions occurring in the primitive solar nebula [START_REF] Grossman | Early chemical history of the solar system[END_REF]. To this end, (i)

the IOM previously synthesized upon octane irradiation was refluxed in water for six months and (ii) a mixture of octane and ethanol was irradiated using the same conditions as those described in the previous chapter. These two experiments led to oxygen incorporation in both soluble and insoluble fractions. Besides, the hydrocarbonaceous constituents of the SOM and of the backbone of the IOM appeared unaffected. However, major differences are observed between the two experiments in the nature of the oxygen-containing products.

Indeed, the compounds released upon reflux of the IOM from irradiated octane were aromatic ketones along with aliphatic and aromatic acids, i. e. the most abundant oxygenated compounds identified in meteorite extracts. Moreover, the IOM was slightly altered by this aqueous heating as reflected by the emergence of FTIR bands related to oxygen functional groups and by the release of benzoic acid, phenol derivative and aromatic ketones upon thermochemolysis. Interestingly, these products were also identified in Murchison pyrolysates. Taken together, the chemical composition of the SOM and IOM after water reflux thus makes hydrothermal alteration a reasonable source of the chondrite oxygen moieties.

In contrast, when the oxygenated compounds are concerned, only one aromatic ketone (benzanthracenone) was identified in the SOM produced upon irradiation of the octane/ethanol mixture and two alcohols (tetrahydronaphthol and biphenylmethanol) in the IOM pyrolysate. As far as we are aware, none of these compounds were reported in the organic matter of carbonaceous chondrites. Initial experiments allow developing the optimal conditions which further are used in all syntheses. In addition the contamination had to be addressed and syntheses with deuterated and unlabeled n-pentane eliminated problem of pollution.

First of all syntheses with pentane, octane and methane supports proposed formation pathway in the gas phase with the condensation of small organic radicals giving rise to aromatic units (Chapter 2). Listed alkanes as precursors of aliphatic radicals spontaneously form aromatic compounds in the cyclization/aromatization process. Moreover, the data highlights the similarity between the IOMs synthesized from both methane and octane which reinforce the ability to produce IOM based on aromatic moieties in plasma of aliphatic hydrocarbons.

The following laboratory manipulations are performed to test the ability of incorporation heteroatoms into macromolecular material from small aliphatic units.

For this purpose two types of precursors of nitrogen are considered: hexylamine as a precursor of nitrogen hybrids and N 2 (Chapter 3). The implemented analytical techniques confirmed that the irradiation experiments with nitrogen precursors led to synthesis of insoluble organic matter containing also nitrogen. Moreover, used spectroscopic methods and elemental analysis confirm that produced organic matters in the laboratory exhibit many similarities to macromolecular materials isolated from Murchison or Orgueil.

Finally to investigate the origin of the oxygen in the macromolecular material isolated from Murchison or Orgueil two pathways are investigated. To verify if either aqueous alteration on the parent body or O incorporation during the organosynthesis are responsible for presence of oxygen in the IOM, synthetic IOM was refluxed in water for 6 months and synthesis involving hydroxyl radicals (ethanol) in addition to the CH x ones are performed. In both experiments we recognized common features with meteoritic IOMs, macromolecular materials are built of highly substituted aromatic moieties linked by short chain aliphatics or less present possible ether linkages. In addition, during the reflux experiment we obtained soluble organic matter which comprise significant amount of compounds containing oxygen, suggesting the origin of the soluble organic matter present in the carbonaceous meteorites. Thus we consider both hypothesis of oxygen incorporationaqueous alteration or the carbonaceous chondrites contain IOM enriched in 15 N compared to terrestrial organic matter it would be interesting verify if any possible isotopic anomalies will occur in the synthesized material in the laboratory.

From the refluxed IOM experiment we can state that macromolecular material is sensible to aqueous alteration and leads to the production of a number of soluble organic compounds containing oxygen. Nevertheless, thermal metamorphism was not investigated here. The influence of temperature on already synthesized IOMs would be asset and could help describe constraints on the environment of accretion of the chondrite parent body and possible metamorphism of the original organic matter.

At the end as a future perspective I would like to answer what is the general picture of IOM formation within an astrophysical scenario, given the evident limits of the experiment presented here.

Finally, from the long term perspectives it remains to define how the organic matter could be associated to prebiotic chemistry. It is important to answer what role this organic matter can play in the beginning and development of life on the primitive Earth.

Fig. 1 . 3

 13 Fig. 1.3 The element abundances of various chondrite groups show depletion pattern related to element volatility. The diagram compares element abundances in ordinary chondrites and CM carbonaceous chondrites, both relative to cosmic CI abundances. The degree of depletion, reflected in the slopes of these trends are distinct[START_REF] Mcsween | Meteorites and Their Parent Planets[END_REF]

Fig. 1

 1 Fig. 1.6 Schematic diagram of protoplanetary disk (Pudritz, Higgs and Stone 2007)

Fig. 1

 1 Fig.1.7 Three possible mechanisms for surface reactions on a regular grain surface. S is the sticking efficiency of a gas-phase species, E D is the binding, or desorption, energy of the adsorbate to the surface, and E b is the barrier from one site to an adjacent one. Empty circles are gas -phase species and full symbols mean atoms or radicals (adsorbates)

  Fig. 1.8 shows suggested reactions which take place in the cold phase by Charnley (Charnley 2001).

Fig. 1

 1 Fig. 1.8 Organic chemistry on interstellar grains resulting from cold H addition reactions to CO. Broken arrows indicate reactions with activation energy barriers; where 2H is shown, a barrier penetration reaction followed by an exothermic addition

Fig. 1 . 9

 19 Fig. 1.9 Examples of different types of carbonaceous materials present in the ISM and Solar System (Ehrenfreund and Charnley 2000) 1.3.2 The Solar System -protoplanetary disk

  Murchison[START_REF] Yuen | Monocarboxylic Acids in Murray and Murchison Carbonaceous Meteorites[END_REF](. These soluble compounds share several molecular properties[START_REF] Pizzarello | The Chemistry of Life's Origin: A Carbonaceous Meteorite Perspective[END_REF]): (1) they have a complete structural diversity (for each formula, every isomer is detected); (2) their abundance decreases as the carbon number increases; (3) in general, branched chains are more abundant than straight chains.

Fig. 1 .

 1 Fig. 1.10 Variety of soluble organics found in the Murchison carbonaceous chondrite (Remusat 2015)

  statistical model of the molecular structure of the IOM Much of our understanding of meteoritic organic matter has come from the investigation of the Murchison meteorite (Fig. 1.14). It is the most representative carbonaceous chondrite which fell in Australia in 1969 and contains a variety of organic molecules. The total collected mass exceeds 100 kg. The meteorite belongs to the CM group. Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body (Airieau et al. 2005).

Fig. 1 .

 1 Fig. 1.14 The picture on the (LEFT) shows a large piece of the Murchison meteorite.(RIGHT) This image is a 'combined X-ray elemental map', created by combining Xray intensities due to magnesium (red), calcium (green) and aluminum (blue) from a thin slice of the Murchison meteorite in an electron microprobe.

Fig. 1 .

 1 Fig. 1.15 Statistical model of molecular structure of the IOM of Murchison proposed by Derenne and Robert (Derenne and Robert 2010).

Fig. 1 .

 1 Fig. 1.16 Ratio of the values for the elemental and molecular parameters listed in Table1.2 calculated from the modeled structure in Fig.1.15 to those experimentally measured in the insoluble organic matter of Murchison[START_REF] Derenne | Model of molecular structure of the insoluble organic matter isolated from Murchison meteorite[END_REF]

Fig. 2 . 1

 21 Fig. 2.1 Scheme of the vacuum line: A pressure gauge, B primary pump, C molecular pump, D U-shaped Pyrex tube, E round bottom flask with reagent, F activated carbon.

  under vacuum for several hours to remove water and other trace gases which may adsorb on the surfaces of the chamber. The influence of several parameters was tested primarily with hydrocarbon precursors to optimize synthesis yield: temperature (345 and 323 K), reaction time (30 and 60 min) and forced power of the microwave (30 and 60 watts). During the microwave discharge, the reaction takes place in the organic plasma and the synthesized organic matter is scraped out of the U-shaped Pyrex tube. The mass balance is achieved by weighting the reaction tube before and after each experiment. Total yield of the reactions is calculated by division of the final mass of the reagent by initial mass of the product multiplied by 100.

Fig. 2

 2 Fig.2.2 Synthesis device showing (a) the microwave discharge and (b) the reaction tube covered with organic residue after synthesis.

Fig 2. 3

 3 Fig 2.3 Schematic structure of GC-MS

Fig. 2

 2 Fig. 2.5 Example of Raman spectra of disordered carbons: charred wood obtained at (a) 1100 °C; (b) 500 °C. Decomposition of spectra into five bands, following the procedure proposed by Sadezky[START_REF] Sadezky | Raman microspectroscopy of soot and related carbonaceous materials: Spectral analysis and structural information[END_REF])and Rouzaud[START_REF] Rouzaud | Carbons at the heart of questions on energy and environment: A nanostructural approach[END_REF]

Fig. 2

 2 Fig. 2.6 Deconvolution of the solid state 13 C NMR spectrum nof the insoluble organic fraction of the Orgueil meteorite recorded with a sample spinning rate of 15 kHz and a contact time of 1 ms[START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF]

Fig. 2

 2 Fig.2.7 EPR spectra at room temperature of the insoluble organic matter of the Orgueil and Murchison meteorites. Microwave power 0.2 mW; microwave frequency 9.5131 GHz; modulation amplitude 0.1 mT; time constant 82 ms; scan rate 0.36 mT.s1. The experimental spectra are compared with pure Lorentzian lineshape functions[START_REF] Binet | Heterogeneous distribution of paramagnetic radicals in insoluble organic matter from the Orgueil and Murchison meteorites[END_REF]

Fig. 2

 2 Fig. 2.8 Diagram of the setup used for the Curie point pyrolysis.

  again focused using a set of objective lenses into an image. The image is then fed down the column through the intermediate and projector lenses, which enlarges the image, depending upon the selected magnification. The darker areas of the image represent the thicker or denser region of the sample where fewer electrons were transmitted and the lighter areas of the image represent those areas which are thinner or less dense.

Fig. 2 . 9

 29 Fig. 2.9 Schematic outline of a TEM.

Fig. 3

 3 Fig.3.1. GC-MS traces of soluble organic matter produced from a) n-pentane, b) fully deuterated n-pentane.

Fig. 3

 3 Fig. 3.3 GC-MS trace of the soluble OM synthesized from n-octane. Numbers refer toTable 3.2.

Fig. 3

 3 Fig. 3.4 Total ion current (TIC) of the 650°C pyrolysate of synthesized IOM from octane. Numbers refer to Table 3.3

Fig. 3

 3 Fig. 3.4 Total ion current (TIC) of the 358°C pyrolysate of synthesized IOM. For identification see Table3.4.

Fig. 3

 3 Fig.3.5 HRTEM observation of synthesized IOM a) and c) raw images and b) and d) corresponding skeletonized images. Raw images obtained with a 500000x magnification (square size: 14 nm x 14 nm).

Fig. 3

 3 Fig. 3.6 Raman spectra of synthesized IOM during irradiation of octane.

Fig. 3 . 7

 37 Fig. 3.7 Raman spectra of synthesized IOM from octane a) -spectrum D and b)spectrum B from Fig. 3.6(after correction of the fluorescence). Spectra are decomposed into bands following the procedure proposed by Sadezky et al (2005) and Rouzaud et al. (2015).

Fig. 3

 3 Fig. 3.8 Decomposition of the solid state 13 C NMR spectrum of the synthesized IOM.

  Fig. 3.9 Solid state 13 C NMR spectra of the synthesized product recorded at various contact time (a) and evolution of the intensities with contact time (b).

Fig. 3 .

 3 Fig. 3.10 FTIR spectrum of the synthesized IOM

Fig. 3 .

 3 Fig. 3.11 TIC of RuO 4 oxidation products of the IOM. The acids are detected as their trimethylsilyl esters. Numbers refer to Table 3.7

Fig. 3 .

 3 Fig. 3.14 Temperature dependence of the spin concentration normalized to the value at 100 K for the IOM of the Orgueil and Murchison meteorites and the terrestrial coals A1 and A2 (data from Binet et al 2004) and synthesized IOM from octane

Fig. 3 .

 3 Fig. 3.15 GC-MS trace of the soluble OM synthesized from methane. Numbers refer to Table 3.9 Contaminants (I -phthalates, II -erucylamide, III -long chain alkanes (C22, C23), IVsiloxanes)

Figure 3 .

 3 Figure 3.18 shows four NanoSIMS images, where A, B, C are related to synthesized IOM from methane and D to IOM isolated from Murchison meteorite. A and B show an isotopically homogeneous region. It must be noted that hydrogen intensity (A) reveals lack of analytical relation between H and D/H ratio image (B). Image C however illustrates regions where the D/H ratio largely exceeds the statistical distribution of D/H ratio recorded in isotopically homogeneous regions.Moreover the same feature is observed in IOM isolated from the Murchison as illustrated on image D where hot spots are shown[START_REF] Thomen | Développement instrumental de la mesure de l'hydrogène, du carbone et de l'azote à la nanosims : applications à l'origine des volatils en cosmochimie[END_REF]). In the IOM from Murchison, the domains appear as spots contrary to the IOM from CH 4 where the domains are rather spread. This is probably due to the fact that in the meteorite the areas are present as distinct grains in the mineralogical matrix and are mechanically mixed with the bulk IOM.

Figure3. 18

 18 Figure3.18 20x20 μm 2 images from NanoSIMS analyses of the D/H ratio expressed in δD units relative to the D/H ratio of the bulk sample (color scale bar for δD ranging from -1000 to +4000‰). Figures A and B show the data collected from the same image of CH 4 plasma deposited IOM and illustrate the routine quality of imaging the D/H ratio. (A) H intensity is expressed in counts per second (B) at the pixel level of

Fig. 3 .

 3 Fig. 3.19 Density distribution of the isotopic compositions of the organic residues deposited from a plasma of a) -CH 4 and b) -octane. Steps of 100‰ rank the δD values. The shaded area represents ≈99% of the sample surface with a domain a variation defined by 2 sigma error (±110‰) around the mean D/H ratio (R0) defining δD =0‰ (δD(‰) = ((R/R0)-1)x1000 with R=D/H). In the case of CH 4 (Fig. a), the chemical reactions responsible for the isotopic compositions of the radicals are

Fig. 3 .

 3 Fig. 3.20 The H/C ratios are reported versus steps δD value of 100‰. The H/C ratio is calculated through a calibration between the ionic currents 12 CH 3 -/ 12 C -and the H/C atomic ratios. The bulk sample value (H/C=1.34) determined by chemical analyses is used for normalization. Error bars on H/C stand for the statistical errors on the 12 CH 3 -/ 12 C -ionic ratio while the 100‰ bars on δD values stand for the width of the step (the +300‰ data point is not reported because of its large errors on the H/C ratio). The figure illustrates the continuous chemical mixing between the different chemical types of IOMs having different molecular compositions and located at different positions in the sample.

  .8) but with different distribution (Fig. 3.22).

Fig. 3 .

 3 Fig. 3.22 Bar diagram comparing the relative abundance of RuO 4 oxidation products in the synthesized (from octane, light grey) and meteorite (Orgueil in grey and Murchison in black) IOM (meteorite data from Remusat(Remusat et al. 2005a). Numbers refer to Table3.7 and isomers of 18 have been distinguished for a better comparison with meteorite data.

  Fig. 3.23. Relationship between relative abundances of pyrolysis products (normalized to 2-methylnaphthalene) from Murchison (a) or Orgueil (b) IOM and IOM synthesized from octane (meteorite data from (Remusat et al. 2005b)). Numbers refer to Table 3.3.

  Fig. 4.1 Principal gas-phase reactions involved in the first stages of nitrogen interstellar chemistry in dark clouds. Nitrogen hydrides (blue, left) and nitriles (red, right) have been clearly separated. The main formation route of NH is highlighted(green). Chemical pathways from nitrogen hydrides to nitriles, which are efficient at specific C/O ratio ranges, are also represented (dashed yellow) (Le[START_REF] Gal | Interstellar chemistry of nitrogen hydrides in dark clouds⋆[END_REF]

  Fig. 4.2 GC-MS trace of the soluble OM synthesized from pure hexylamine (a) and noctane / hexylamine mixture (b). Numbers refer to Table 4.1

Fig. 4 . 3

 43 Fig. 4.3 Bar diagram comparing the relative abundance of N-containing compounds (normalized to pyrene) in SOM from pure hexylamine and hexylamine/octane mixture.

  Fig 4.5b) reveals a minor contribution at 58 ppm which was not observed in the spectrum of the IOM synthesized from octane and was therefore assigned to aliphatic C linked to nitrogen. The peak at 110-180 ppm contains at least two contributions corresponding to sp 2 -bonded carbon atoms. The most prominent peak at 126 ppm is mainly attributed to protonated aromatic. The signal at 140 ppm corresponds to non-protonated aromatic C. A shoulder at 162 ppm which was lacking in the spectrum of the IOM obtained from octane is present and it is assigned to sp 2 C in heterocycles. The presence of aliphatic C derived from NMR is confirmed by FTIR spectra (Fig. 4.6 a and b ) which show aliphatic C-H stretching absorptions at 2925 cm -1 and symmetrical CH 3 and asymmetrical CH 2 and CH 3 bending vibrations at 1376 cm -1 and 1450 cm -1 , respectively. This feature was also observed in the product produced from octane (Fig 4.6 c). The aromatic character is evidenced by the 1606-1620 cm -1 band which should include C=C and C=N stretching vibrations. The spectra of the two IOMs from hexylamine and hexylamine/octane mixture show a band at 2217 cm -1

  Fig. 4.5 a) Solid state 13 C NMR spectra of the synthesized IOM from: hexylamine (NS=4212) and hexylamine/octane mixture (NS=82224). b) Decomposition of the spectrum of the IOM from the hexylamine/octane mixture. SSB stands for spinning side band of the aromatic peak, the symmetrical SSB falling in the aliphatic peak area

Fig. 4

 4 Fig. 4.9 Bar diagram comparing the relative abundance of N-containing compounds between the two IOM (pure hexylamine and hexylamine/octane mixture).

Fig. 4 .

 4 Fig. 4.10 GC-MS trace of the soluble OM synthesized from n-octane + N 2 . Numbers refer to Table 4.3

Fig. 4 .

 4 Fig. 4.11 Comparison between relative abundances of SOM products (normalized to phenanthrene) from octane with N 2 and pure octane.

Fig. 4

 4 Fig. 4.12 (a) Solid state 13 C NMR spectra of the synthetized products made from: octane and N 2 (NS = 23800) and octane (b) Decomposition of the solid state 13 C NMR spectrum of the synthesized IOM from molecular nitrogen and octane; SSB stands for side spinning bands

Fig. 4 .

 4 Fig. 4.13 FTIR spectrum of insoluble organic fraction of the material produced from a)octane and b) -octane + N 2

Fig. 4 .

 4 Fig. 4.15 Relationship between relative abundances of Py GC-MS products (normalized to 2-methylnaphthalene) from IOM synthesized from octane with N 2 and pure octane.

Fig. 5

 5 Fig. 5.1. GC-MS trace of the silylated soluble compounds released after 24h reflux of IOM synthesized from deuterated n-pentane

  16), phenalenone (17) and cyclopentaphenanthrenone (18) which are easily related to their hydrocarbonaceous counterparts. The latter were identified among the pyrolysis products of the IOM (section 3.2.4).The occurrence of these oxygenated compounds and their structure relationship with the aromatic moieties of the IOM demonstrates the ability of the hot water to alter this hydrocarbonaceous macromolecule. As the IOM is used as a model for the hydrocarbon backbone of the chondrite IOM, we have looked for the presently released products in meteorite extracts.

Fig. 5

 5 Fig. 5.2 GC-MS trace of the silylated soluble compounds released after 6 month reflux of IOM synthesized from n-octane. Numbers refer to Table 5.1 * -contaminant (trimethylsilyl ether of glycerol)-present also in refluxed deuterated IOM (Fig. .) ** -contamination (plasticizers: phthalate and erucylamide)

  Elemental analysis revealed some oxygen incorporation in the IOM with O/C 0.09 and a subsequent decrease in H/C from 1.11 to 0.95. Although lower than that of chondrite IOM, the O/C ratio points to oxygen incorporation into the IOM upon water reflux. FTIR was thus used to track potential changes in the chemical functions.

Fig. 5

 5 Fig. 5.3 FTIR spectra of starting IOM (a) and refluxed IOM for 6 months in water (b)

Fig. 5

 5 Fig. 5.5 GC-MS trace of soluble OM synthesized from n-octane:ethanol 1:4 mixture. Numbers refer to Table5.3

Fig. 5

 5 Fig. 5.6 FTIR spectra of IOM synthesized from (a) octane:ethanol 1:4 mixture and (b) pure octane

Fig. 5 .

 5 Fig. 5.7 a) Solid state 13C NMR spectra of the synthesized IOM from: octane (Biron et al. 2015) and mixture of octane/ethanol (v:v 1:4). b) Decomposition of the spectrum of the IOM from the ethanol/octane mixture. SSB stands for spinning side band of the aromatic peak, the symmetrical SSB falling in the aliphatic peak area

Fig. 5

 5 Fig. 5.8 TIC pyrochromatogram of the IOM synthesized from a mixture of ethanol and octane. Numbers refer to Table 5.4 * -contamination from previous experiment

  accepted that carbonaceous chondrites preserved a record of the chemistry that occurred during the formation of the Solar System. Thus understanding of the origin of the organic material from meteorites is a fundamental goal but also a daunting task. Insoluble organic material, as the most carbon occurs in this fraction, has presented a series of analytical challenges. Nevertheless recently Derenne and Robert proposed a model of the molecular structure for the IOM of Murchison (Derenne and Robert 2010). As up to now, the chemical and physical properties of IOM are still poorly known which cause a poor understanding of the initial organic synthesis process. Thus inspired by model suggested by Derenne and Robert the aim of this research was to put forward the mysterious synthesis pathway of OM similar to the one isolated from Murchison or Orgueil.This work has been achieved by performing series of syntheses where different reagentsprecursors of small aliphatic units, were used in order to, firstly test the mechanism proposed by Derenne & Robert and secondary incorporate heteroatoms in the macromolecular material. For this purpose the microwave plasma, is used as a source of UV radiation of organic compounds and electrons which are highly reactive. This kind of setup, simulating early solar nebula processes, led to eventually formation of organic matters which are further extracted and separated into insoluble residue (IOM) and soluble organic matter (SOM). The produced organic solids are characterized ex-situ by a variety of analytical techniques such as GC-MS, Py GC-MS upon methylation and sylilation, elemental analysis, FTIR, Solid state 13 C NMR, EPR, Ruthenium Tetroxide Oxidation (RuO 4 oxidation), Raman Micro-spectroscopy, HRTEM and NanoSIMS (Chapter 3, 4 and 5).

Table 3 .

 3 1 Influence of the various parameters on the yield of synthesized OM.

	Alkane	Temperature	Power	Reaction time	Total yield
		(°C)*	(watt)	(min)	(%)
	n-pentane	72	30	30	0.3
	n-pentane	50	60	30	3.9
	n-pentane	72	60	30	5.3
	n-pentane	72	60	60	6.8
	n-octane	72	60	30	10.1
	n-octane	72	60	60	15.3

Table 3 .

 3 2 List of GC-MS identified compounds in the soluble OM synthesized from noctane.

	Number	Compound
	1	Naphthalene
	2	2-methylnaphthalene
	3	1-methylnaphthalene
	4	1-ethylnaphthalene
	5	Biphenylene
	6	Biphenyl
	7	Acenaphthylene
	8	Acenaphthene
	9	C 3 -alkylnaphtalene
	10	Phenalene
	11	Fluorene
	12	9-methylfluorene
	13	2-methylfluorene
	14	1-methylfluorene
	15	Phenanthrene
	16	Anthracene
	17	2-methylphenanthrene
	18	1-methylphenanthrene
	19	Cyclopentaphenanthrene
	20	Fluoranthene
	21	Pyrene
	22	Benzofluorenes
	23	Methylpyrenes
	24	Benzofluoranthene
	25	Cyclopentapyrene
	26	Dihydrocyclopentapyrene

Table 3 . 3 Table 3 .

 333 3 List of identified compounds released upon 650°C pyrolysis of the synthesized IOM and of Murchison and Orgueil meteorites.

	Number

Table 3

 3

	.4 List of identified compounds released upon 358°C pyrolysis of the
	synthesized IOM
	Number	Compound detected by 358°C Py GC-MS in IOM	Compound detected by 650°C Py GC-MS in IOM	Compound detected by GC-MS in SOM
	1	Heptane	-	-
	2	Toluene	+	-
	3	Octane	-	-
	4	C2-alkylbenzene	+	-
	5	C3-alkylbenzenes	+	-
	6	Indane	+	-
	7	Indene	+	-
	8	C4-alkylbenzene	+	-
	9	C5-alkylbenzene	+	-
	10	Methylindene	+	-
	11	Naphthalene	+	+
	12	Dihydromethylnaphthalene	-	-
	13	2-methylnaphthalene	+	+
	14	1-methylnaphthalene	+	+
	15	C2-alkylnaphthalene	+	+
	16	Acenaphthylene	+	+
	17	Acenaphthene	+	+
	18	C3-alkylnaphthalene	+	+
	19	Fluorene	+	+
	20	Methylfluorene	-	+
	21	Phenanthrene	+	+
	22	Cyclopentaphenanthrene	-	+

Table 3

 3

.5 Average structural parameters of the aromatic units in the synthesized IOM.

L -

average length [nm] single layer % d -interlayer spacing [nm]

	Amorphous-like
	carbon	0.39	84	0.41
	Disordered carbon	0.48	69	0.39

Table 3 .

 3 6 Relative abundances of the different types of C calculated from the CP/MAS 13 C NMR spectra in the synthesized IOM.

	Carbon type	δ (ppm)	relative abundances (%)	Total (%)
	Ali-linked CH 3	14	8
	Aro-linked CH 3	23	6	52
	CH 2	35	38
	protonated aromatic C non-protonated aromatic C	126 139	29.5 18.5	48

Table 3 . 7 Table 3 .

 373 7 Compounds identified through RuO 4 oxidation of synthesized IOM

	Number	Compound Synthesized IOM	Murchison*	Orgueil*
	1	isomers of pentanoic acid	-	-
	2	n-pentanoic acid	-	-
	3	isomers of hexanoic acid	-	-
	4	n-hexanoic acid	-	-
	5	isomers of heptanoic acid	-	-
	6	cyclopentanecarboxylic acid	-	-
	7	ethanedioic acid	+	+
	8	4-oxopentanoic acid	-	-
	9	isomers of octanoic acid	-	-
	10	n-heptanoic acid	-	-
	11	isomers of nonanoic acid	-	-
	12	5-oxohexanoic acid	-	-
	13	benzoic acid	+	+
	14	n-octanoic acid	-	-
	15	cyclohexanecarboxylic acid	-	-
	16	butanedioic acid	+	+
	17	isomers of pentanedioic acid	+	+
	18	isomers of hexanedioic acid	+	+
	19	6-oxoheptanoic acid	-	-
	20	isomers of decanoic acid	-	-
	21	n-nonanoic acid	-	-
	22	pentanedioic acid	+	+
	23	n-decanoic acid	-	-
	24	isomers of heptanedioic acid	+	+
	25	hexanedioic acid	+	+
	26	heptanedioic acid	-	+
	27	benzenedicarboxylic acid	+	+
	28	octanedioic acid	-	+
	29	nonanedioic acid	-	+

*

(Remusat et al. 2005a)

Table 3

 3

	No.	Compound
	1	4-oxopentanoic acid
	2	Butanedioic acid
	3	Isomer of pentanedioic acid
	4	4-oxohexanoic acid
	5	Isomers of hexanedioic acid
	6	5-oxohexanoic acid
	7	Pentanedioic acid
	8	Isomer of heptanedioic acid
	9	Hexanedioic acid
	10	Isomer of octanedioic acid
	11	Heptanedioic acid
	12	Octanedioic acid
	13	Propanetricarboxylic acid
	14	Benzenedicarboxylic acid
	15	Butanetricarboxylic acid
	16	Nonanedioic acid
	17	Benzenetricarboxylic acids

.8 Compounds identified through RuO 4 oxidation of synthesized insoluble organic matter upon methylation procedure. Compounds which were not detected with silylation are indicated in bold

Table 3 .

 3 9 GC-MS identified compounds in the soluble OM synthesized from methane.

	No.	SOM synthesized from methane	SOM synthesized from octane
		Naphthalene	+
		2-methylnaphthalene	+
		1-methylnaphthalene	+
		Ethylnaphththalene	+
		Biphenylene	+
		Acenaphthylene	+
		Acenaphthene	+
		Phenalene	+
		Fluorene	+
		Methylfluorene	+
		Phenanthrene	+
		Anthracene	+
		2-methylphenanthrene	+
		1-methylphenanthrene	+
		Cyclopentaphenanthrene	+
		Fluoranthene	+
		Pyrene	+
		Benzofluorenes	+
		Methylpyrene	+
		Cyclopentapyrene	+

Table 3 .

 3 10 List of identified compounds released upon 650°C pyrolysis of the synthesized IOM from methane and comparison with the octane experiment

	Compound

Table 4 . 1 Table 4 .

 414 1 GC-MS identified compounds in the soluble organic matter synthesized from pure hexylamine and hexylamine/octane mixture. N-containing compounds are reported in bold

	PEAK NO. Compounds in SOM obtained from	HEXYLAMINE	OCTANE + HEXYLAMINE
	Hexylamine	+	-
	Methyl C2-alkylpiperidine	+	-
	Methylindene	-	+
	Naphthalene	+	+
	Benzenedicarbonitriles	+	+
	Methylnaphthalene	-	+
	Methyl C6-alkylpiperidine	+	-
	Toluenedicarbonitrile	-	+
	Cyanobenzeneacetonitriles	+	+
	Biphenylene	+	-
	Biphenyl	+	+
	Acenaphthylene	+	+
	Acenaphthene	+	+
	Naphthalenecarbonitriles	+	+
	Benzenetricarbonitrile	+	-
	Phenalene	+	+
	Fluorene	+	+
	Methylnaphthalenecarbonitriles	+	+
	C2-alkylbiphenyl	-	+
	Naphthaleneacetonitrile	+	-
	Methylfluorenes	-	+
	Benzo(iso)quinolines	+	+
	Benzenetetracarbonitrile	+	-
	Phenantrene	+	+
	Anthracene	-	+
	Acridine	+	-
	Fluorenecarbonitriles	+	+
	Methylphenanthrene	-	+
	Cyclopentaphenanthrene	+	+
	Fluoranthene	+	+
	Anthracenecarbonitrile	+	-
	Pyrene	+	+
	Benzofluorenes	+	+
	Methylpyrenes	+	+
	C2-alkylpyrene	-	+
	Benzofluoranthene	+	+
	Cyclopentapyrene	+	-
	Dihydrocyclopentapyrene	+	+

Table 4 . 3 Table 4 .

 434 3 List of GC-MS identified compounds in the IOM synthesized from octane + N 2 .

	PEAK NO.	Compounds in SOM
	Methylnaphthalenes
	Ethylnaphthalene
	Biphenylene
	Biphenyl
	Acenaphthylene
	Acenaphthene
	Naphthalenecarbonitriles
	C3-alkylnaphthalene
	Phenalene
	Fluorene
	Methylfluorenes
	C2-alkylbiphenyl
	Phenantrene
	Anthracene
	Methylphenanthrenes
	Methylanthracene
	Cyclopentaphenanthrene
	Phenylnaphthalene
	Fluoranthene
	Pyrene
	Benzofluorenes
	Methylpyrenes
	Benzofluoranthene
	Cyclopentapyrene
	Dihydrocyclopentapyrene

Table 4 .

 4 4 List of Py-GC-MS identified compounds in the insoluble organic matter synthesized from octane + N 2 .

	Peak numner	Name of the compound
	1	Toluene
	2	Octane
	3	Ethylbenzene
	4	1,4-dimethylbenzene
	5	1,2-dimethylbenzene
	6	C3-alkylbenzenes
	7	Indane
	8	Indene
	9	Methylbenzonitrile
		C4-alkylbenzenes
		C5-alkylbenzenes
		Methylindenes
		Naphthalene
		C2-alkylindane
		Methyldihydronaphthalenes
		C2-alkylindene
		2-methylnaphthalene
		1-methylnaphthalene
		Biphenyl
		C2-alkylnaphthalenes
		Acenaphthylene
		Acenaphthene
		C3-alkylnaphthalene
		Naphthalenecarbonitrile
		Phenalene
		Methylbiphenyl
		Fluorene
		C2-alkylbiphenyls
		C3-alkylbiphenyl
		Phenanthrene
		Fluoranthene
		Pyrene

  [START_REF] Gardinier | Solid state CP/MAS 13C NMR of the insoluble organic matter of the Orgueil and Murchison meteorites: quantitative study[END_REF]), the origin of which remains unclear. Two main pathways can be put forward to account for this oxygen content depending on the time of O incorporation with respect to IOM formation: either aqueous alteration on the parent body(Kerridge and Bunch 1979, Zolensky and[START_REF] Zolensky | Meteorites and the early solar system[END_REF] or O incorporation[START_REF] Grossman | Early chemical history of the solar system[END_REF] during the organosynthesis. It must be noted that these pathways are not mutually exclusive. Evidence for various degree of alteration in all major chondrite groups is given by the presence of hydrous minerals such as phyllosilicates or sulfates. The variable alterations existing in chondrites are the results of processes occurring under different conditions (variable temperature,

	5 Aqueous alteration & incorporation of oxygen
	5.1 Introduction
	Insoluble organic matter (IOM) in meteorites is characterized by substantial
	contents in oxygen (O/C ratio of 0.18 and 0.22 for Orgueil and Murchison,
	respectively,(

Table 5 .

 5 1 List of GC-MS identified compounds released after 6 month water reflux of IOM synthesized from n-octane. Oxygen-containing compounds are indicated in bold

	No.	Compounds
	1	Hydroxypropanoic acid
	2	Phenol
	3	Benzoic acid
	4	Indanone
	5	Butanedioic acid
	6	Isomer of pentanedioic acid
	7	Methylbenzoic acid
	8	Isobenzofuranone
	9	Pentanedioic acid
		Trimethylbenzoic acid
		Methylnaphthyl ketone
		Benzenedicarboxylic acid
		Fluorenone
		Naphthalenecarboxylic acid
		Phenanthrene
		Anthrone
		Phenalenone
		Cyclopentaphenanthrenone
		Fluoranthene
		Pyrene
		Methylpyrenes
		Phenylphenanthrene

Table 5 .

 5 2 List of identified compounds released upon 650°C pyrolysis in the presence of TMAH of the 6 month refluxed IOM. Oxygen-containing compounds are indicated in bold

	No.	Compounds	IOM before reflux	Murchison	Orgueil
	1	Toluene	+	+	+
	2	Octane	-	-	-
	3	C2-alkylbenzenes	+	+	+
	4	C3-alkylbenzenes	+	+	+
	5	Indane	+	+	-
	6	Indene	+	+	+
	7	C4-alkylbenzene	+	+	+
	8	Acetophenone	-	+	+
	9	Benzoic acid	-	-	-
	10	Dimethylanisole	-	-	-
	11	C5-alkylbenzene	+	-	-
	12	Methylindene	+	+	+
	13	Naphthalene	+	+	+
	14	C6-alkylbenzene	-	-	-
	15	Methyldihydronaphthalene	+	-	+
	16	2-methylnaphtalene	+	+	+
	17	1-methylnaphtalene	+	+	+
	18	C3-alkylindene	-	-	-
	19	C2-alkylnaphthalenes	+	+	+
	20	Acenaphthylene	+	+	+
	21	C3-alkylnaphthalenes	+	+	+
	22	Phenalene	+	+	+
	23	Methylfluorene	+	+	+
	24	Anthracene	+	+	+

Table 5 .

 5 3 List of GC-MS identified compounds of soluble OM synthesized from noctane:ethanol 1:4 mixture.

	No.	Compound	synthesized SOM from octane
	1	Phenalene	+
	2	Methylfluorenes	+
	3	Phenanthrene	+
	4	Anthracene	+
	5	2-methylphenanthrene	+
	6	1-methylphenanthrene	+
	7	Cyclopentaphenanthrene	+
	8	Phenylnaphthalene	-
	9	Fluoranthene	+
	10	Pyrene	+
	11	Benzofluorenes	+
	12	Methylpyrenes	+
	13	Benzofluoranthene	+
	14	Benzoanthracene	-
	15	Cyclopentapyrene	+
	16	Dihydrocyclopentapyrene	+
	17	Benzoanthracenone	-
	18	Methylbenzophenanthrenes	-
	19	Benzofluoranthene	-
	20	Dihydrobenzopyrene	-
	21	Indenopyrene	-

Table 5 .

 5 4 . List of identified compounds released upon 650°C pyrolysis of the IOM synthesized from a mixture of octane and ethanol

	No.	Compound	IOM synthesized from octane Murchison	Orgueil
	1	Toluene	+	+	+
	2	Octane	-	-	-
	3	Ethylbenzene	+	+	+
	4	1,4-dimethylbenzene	+	+	+
	5	1,3-dimethylbenzene	+	+	+
	6	1,2-dimethylbenzene	+	-	-
	7	C3-alkylbenzenes	+	+	+
	8	Indane	+	+	-
	9	Indene	+	+	+
	10	C4-alkylbenzenes	+	+	+
	11	C5-alkylbenzene	+	-	-
	12	Methylindenes	+	+	+
	13	Tetrahydronaphthol	-	-	-
	14	Naphthalene	+	+	+
	15	C2-alkylindene	+	-	-
	16	Methyldihydronaphthalene	+	-	+
	17	2-methylnaphthalene	+	+	+
	18	1-methylnaphthalene	+	+	+
	19	Biphenyl	+	+	+
	20	C2-alkylnaphthalenes	+	+	+
	21	Acenaphthylene	+	+	+
	22	Acenaphthene	+	+	+
	23	C3-alkylnaphthalenes	+	+	+
	24	Biphenylmethanol	-	-	-
	25	Phenalene	+	+	+
	26	Fluorene	+	+	+
	27	C2-alkylbiphenyl	+	-	-
	28	Phenanthrene	+	+	+
	29	Anthracene	+	+	+
	30	Fluoranthene	+	+	+
	31	Cyclopentaphenanthrene	+	-	-
	32	Pyrene	+	+	+

* This section is based on a paper published in Meteoritics and Planetary Science.

Acknowledgements Firstly, I would like to express my sincere gratitude to my advisors Sylvie Derenne and François Robert for their support and related research, for their patience, and immense knowledge. Their guidance helped me in all the time of research and writing of this thesis. I could not have imagined having such a good mentors for my PhD study. Besides my advisors, I would like to thank the rest of my thesis committee: Pierre Adam and Louis Le Sergeant d'Hendecourt for being my reporters and Nathalie Carrasco and Bernard Marty -my advisors in "comité de thèse" for their insightful comments and encouragement, critical evaluation of this work, and more importantly, their time. My sincere thanks also goes to Christelle Anquetil, Adriana Gonzalez -Cano and Remi Duhamel, without who I would never understand the engineering side of my research. Without their precious support it would not be possible to conduct this project. Also I am thankful to Jean-Noel Rouzaud and Laurent Binet for sharing their knowledge, critical scientific input and help in this research project.

I thank my fellow labmates (Agnieszka, Alice and Sarah) for the stimulating discussions and mostly for all the fun we have had in the last three and an half years.

Last but not the least, I would like to thank my family: my mum, my husband and to my sister for supporting me spiritually throughout writing this thesis and my life in general….

Synthesis of organic matter containing carbon and hydrogen

Moreover, a D5 band, attributed to the presence of hydrocarbons trapped within the organic networks, was revealed by Raman micro-spectroscopy. This trapping in the synthesized IOM is in agreement with the aforementioned data of pyrolysis especially those obtained at 358°C. The same phenomenon was reported in meteorites with aromatic hydrocarbons ranging from benzene to pyrene, which could be thermally extracted at temperatures at or below 300 °C can be liberated [START_REF] Studier | Origin of organic matter in early solar system-I. Hydrocarbons[END_REF].

The aforementioned NanoSIMS data experimentally show that the polymerization of organic radicals can yield isotopic heterogeneities in the D/H ratio of the condensed organic matter, heterogeneities commensurable with those observed in the chondritic IOM. In addition, they account for the simultaneous occurrence of hot and cold spots that are also commonly observed at a micrometer spatial resolution in the IOM. Indeed, the Murchison meteorite was shown to exhibit 1±0.5 m size cold and hot spots with D values, expressed relative to the bulk composition of the IOM (D = +970‰ relative to SMOW) ranging from -725‰ to +1390‰. A chemistry involving radicals would account for (1) the isotope exchange reaction between CH 3

• and H • and (2) the IOM condensation which would yield both isotopic hot and cold spots. Although the physical process at the origin of the production of organic radicals in the protosolar disk should still be considered as an open issue, the significant isotopic fractionation associated with polymerization reactions of organic radicals must be considered as a possible additional process playing a role in the deuterium enrichment observed in solar system organic compounds. Moreover, when the relative abundances of the hydrocarbons identified in the pyrolysates of the three IOMs: pure hexylamine, hexylamine/octane mixture and Moreover, the aromatic C=C band observed at 1600 cm -1 tends to broaden, likely due to the presence of C=N groups. The other bands, corresponding to stretching of aliphatic C-H (around 2900 cm -1 ) and to the asymmetric bending mode of CH 3 and CH 2 groups at 1450 cm -1 and symmetric bending mode of CH 3 groups at 1375 cm -1 do not appear affected by the presence of nitrogen.

Synthesis and analysis of organic matter containing nitrogen

The insoluble organic matter was analyzed with Curie point pyrolysis in order to characterize IOM at the molecular level thus allowing a precise comparison with the IOM from octane. All but one pyrolysis products are aromatic hydrocarbons which comprise from one (1-6) up to four (32) rings.

Aqueous alteration & incorporation of oxygen

Conclusions and future perspectives

formation of IOM with the participation of aliphatic units which also contained oxygen possible according to accomplished laboratory manipulations.

To this end, NanoSIMS data experimentally shows that the polymerization of organic radicals can yield isotopic heterogeneities in the D/H ratio of the condensed organic matter, heterogeneities commensurable with those observed in the chondritic IOM. In addition, they account for the simultaneous occurrence of hot and cold spots that are also commonly observed at a micrometer spatial resolution in the IOM. Thus the significant isotopic fractionation associated with polymerization reactions of organic radicals may be considered as a possible additional process playing a role in the deuterium enrichment observed in solar system organic compounds.

Future perspectives

The macromolecular material consists carbon and hydrogen as well as heteroelements: oxygen, nitrogen and sulfur. Current syntheses allowed to incorporate the oxygen and the nitrogen. Further manipulations should thus require synthesis of IOM containing sulfur. For this purpose, a reagent such as carbon disulfide in the mixture with other alkanes may be considered or elemental sulfur. The identical set of analytical methods should be implemented in order to verify synthesized product.

The involvement of a possible catalyst in the condensation reactions may be also planned in the future work. The presence of small amounts of for instance magnesium silicates could favorably accelerate the rate of some chemical reaction and possibly improve its yield. In addition, this kind of manipulation could explain the problem of association of IOM with the silicate grains as it is the case in meteorites and also possibly establish a chronology between the synthesis of IOM, its isotope enrichment and its relation with the silicate in the meteorites parent body.

As the study presented in this thesis includes the NanoSIMS analysis of the IOM comprising only carbon and hydrogen elements it would be worth also consider the IOMs where the nitrogen is incorporated into the macromolecular material. As the