Géraldine Féraud

Luis Domenianni

Ernesto Marceca
email: marceca@qi.fcen.uba.ar

Claude Dedonder- Lardeux

Christophe Jouvet
email: christophe.jouvet@univ-amu.fr

Photodissociation Electronic Spectra of Cold Protonated Quinoline and Isoquinoline in the Gas-Phase

Photofragmentation electronic spectra of isolated single-isomeric N-protonated quinoline (quinolinium) and isoquinoline (isoquinolinium) ions have been measured at a temperature of 40 K using a mass-selective, 10 cm 1 spectral resolution, photodissociation spectrometer.

 together with TD-DFT calculations and a careful analysis of the possible fragmentation mechanisms. This information will be complemented in the present study by appending better resolved spectra, characteristic of cold ions, in which well-defined vibrational progressions associated to the S 1 S 0 and S 3 S 0 transitions exhibit clear 00 bands at h 00 = 27868 and 42230 cm 1 , for protonated quinoline, and at h 00 = 28043 and 41988 cm 1 , for protonated isoquinoline. Active vibrations in the spectra were assigned with the help of calculated normal modes, looking very similar to those of the structurally related protonated naphthalene. Finally, we have observed that the bandwidths associated with the deep-UV S 3 S 0 transition denote a lifetime for the S 3 excited state in the subpicosecond time scale, in contrast with that of S 1 .

Introduction:

Polycyclic aromatic nitrogen heterocycles (PANHs) involve a group of compounds widely distributed in the Earth´s biosphere 1 as a consequence of the emission caused by natural fires, incomplete combustion of fuels and discharge of industrial effluents, among other sources. 2,3 The toxicity of several PANHs, 4 normally exceeding that of the structurally related polycyclic aromatic hydrocarbons (PAHs), has motivated the development of analytical methods that, in many cases, must rely on the scarce photophysical information existing for these molecules. [START_REF] Tucker | Polycyclic Aromatic Nitrogen Heterocycles. Part V: Fluorescence Emission Behavior of Select Tetraaza-and Diazaarenes in Nonelectrolyte Solvents[END_REF] Additionally, many authors have hypothesized [START_REF] Ricca | Mechanism for the Incorporation of a Nitrogen Atom into Polycyclic Aromatic Hydrocarbon Cations[END_REF][START_REF] Bernstein | Laboratory Infrared Spectra of Polycyclic Aromatic Nitrogen Heterocycles: Quinoline and Phenanthridine in Solid Argon and H 2 O[END_REF][START_REF] Hudgins | Variations in the Peak Position of the 6.2 μm Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population[END_REF] that PANHs might also exist beyond the Earth throughout the interstellar medium (ISM), as a result of the reaction between interstellar nitrogen and PAHs. The presence of PAHs in the ISM has long been postulated to account for absorption features in the diffuse interstellar bands (DIBs) [START_REF] Van Der Zwet | Polycyclic Aromatic Hydrocarbons and the Diffuse Interstellar Bands[END_REF][START_REF] Léger | Are Polycyclic Aromatic Hydrocarbons the Carriers of the Diffuse Interstellar Bands in the Visible?[END_REF][START_REF] Crawford | Ionized Polycyclic Aromatic Hydrocarbons and the Diffuse Interstellar Bands[END_REF] and emission features in the aromatic infrared bands (AIBs). [START_REF] Allamandola | Interstellar Polycyclic Aromatic Hydrocarbons -The Infrared Emission Bands, the Excitation/Emission Mechanism, and the Astrophysical Implications[END_REF] More recently, it was pointed out using experimental and theoretical arguments that the AIBs' assignment is improved by considering nitrogen-containing PAHs. [START_REF] Hudgins | Variations in the Peak Position of the 6.2 μm Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population[END_REF][START_REF] Tielens | Interstellar Polycyclic Aromatic Hydrocarbon Molecules[END_REF][START_REF] Mattioda | Near-Infrared Spectroscopy of Nitrogenated Polycyclic Aromatic Hydrocarbon Cations from 0.7 to 2.5 μm[END_REF][START_REF] Galué | Gas-phase Infrared Spectra of Cationized Nitrogen-Substituted Polycyclic Aromatic Hydrocarbons[END_REF][START_REF] Boersma | Properties of Polycyclic Aromatic Hydrocarbons in the Northwest Photon Dominated Region of NGC 7023. I. PAH Size, Charge, Composition, and Structure Distribution[END_REF] Nevertheless, very few gas phase electronic spectra are available to conclusively establish whether the visible absorption of PANH + s is part of the observed astronomical DIBs. [START_REF] Dryza | Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline + and Quinoline +[END_REF] In addition to the radical cations, protonated PANHs (hereafter PANHH + s) will likely be found in the ionized environments of the ISM due to the high proton affinity of the aromatic nitrogen expected for these molecules. Evidence supporting this assumption was given by recent IR measurements [START_REF] Galué | Gas-phase Infrared Spectra of Cationized Nitrogen-Substituted Polycyclic Aromatic Hydrocarbons[END_REF] performed on four small-size PANHH + s that were found to reproduce closely the 6.2 m and 8.6 m AIBs. However, well resolved electronic spectra of isolated PANHH + s are still needed [START_REF] Noble | The Electronic Spectra of Protonated PANH Molecules[END_REF] to explore if the visible absorption of these ions is a component of the DIBs.

In this work we have measured the photodissociation electronic spectra of cold protonated quinoline and isoquinoline, the two simplest PANHH + s comprising a pyridinium cation fused to a six-membered carbocyclic ring. Both quinoline and isoquinoline are structurally related to naphthalene, being one CH group of the latter molecule substituted by one aromatic nitrogen atom at positions 1 and 2, respectively (Scheme 1). Protonation occurs on the nitrogen sp 2 lone electron pair leading to the corresponding quinolinium (QH + ) or isoquinolinium (iQH + ) cations, as shown in Scheme 1. C-protonation is highly disfavored due to the electron deficiency at the aromatic carbons caused by the inductive polarization of the electronegative heteroatom.

Even though the electronic spectroscopic properties of neutral quinolines [START_REF] Wanna | van der Waals Clusters of Pyridazine and Isoquinoline: The Effect of Solvation on Chromophore Electronic Structure[END_REF][START_REF] Hiraya | Identification of the Lowest Energy n* States in Gas-Phase Polycyclic Monoazines: Quinoline and Isoquinoline[END_REF][START_REF] Hiraya | Multiphoton Ionization Photoelectron Spectroscopy of Molecular Excited States in Supersonic Jet: Low-Lying Electronic States of Isoquinoline[END_REF][START_REF] Bouwman | Dissociative Photoionization of Quinoline and Isoquinoline[END_REF] and their radical cations [START_REF] Dryza | Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline + and Quinoline +[END_REF] have been extensively studied in the gas phase, less information is available on the corresponding isolated protonated molecules. [START_REF] Klaerke | UV Action Spectroscopy of Protonated PAH Derivatives. Methyl Substituted Quinolines[END_REF][START_REF] Hansen | Ultraviolet Photodissociation Action Spectroscopy of Gas-Phase Protonated Quinoline and Isoquinoline Cations[END_REF] In particular, only one spectrum at room temperature has been obtained for QH + and iQH + using photodissociation action spectroscopy by Hansen et al., [START_REF] Hansen | Ultraviolet Photodissociation Action Spectroscopy of Gas-Phase Protonated Quinoline and Isoquinoline Cations[END_REF] and so far well resolved vibronic spectra of cold ions are still lacking. A careful analysis of the fragmentation mechanism has been done in the paper by Hansen et al., and we will use their calculations for further discussion. We will present new UV-vis spectroscopic data for QH + and iQH + in which we were able to improve the accuracy of the electronic band origins, exhibit well resolved vibrational progressions associated to the low lying excitations, and provide estimations about the lifetime of the excited states based on the observed line broadenings. All the measurements were performed using a cryogenic ion trap photodissociation spectrometer in which the ions can be cooled to temperatures of a few tens of Kelvin. Pump-probe UVUV ion-dip experiments [START_REF] Féraud | Development of Ultraviolet-Ultraviolet Hole-Burning Spectroscopy for Cold Gas-Phase Ions[END_REF] were employed to explore the contribution of possible tautomers in the spectral bands. The photochemical processes observed for protonated quinoline and isoquinoline will be compared with former measurements on protonated naphthalene. [START_REF] Alata | Effect of Protonation on the Electronic Structure of Aromatic Molecules: NaphthaleneH +[END_REF][START_REF] Alata | Role of the Charge-Transfer State in the Electronic Absorption of Protonated Hydrocarbon Molecules[END_REF] To support the spectroscopic observations, ab-initio calculations were performed on QH + and iQH + ground and excited states.

Methods:

Electronic spectra were recorded using the same experimental set-up as in previous work. [START_REF] Alata | Electronic Spectra of the Protonated Indole Chromophore in the Gas Phase[END_REF][START_REF] Kang | New Method for Double-Resonance Spectroscopy in a Cold Quadrupole Ion Trap and Its Application to UV-UV Hole-Burning Spectroscopy of Protonated Adenine Dimer[END_REF] Only a brief description of the apparatus will be given here, including the ions' preparation method and the applied spectroscopic techniques. Parent QH + and iQH + ions are formed in an electrospray source fed by a continuum flow of an acidulated water/methanol mixture (1:1 in volume) in which the corresponding quinoline is dissolved at a concentration Additionally, a double resonance method [START_REF] Kang | New Method for Double-Resonance Spectroscopy in a Cold Quadrupole Ion Trap and Its Application to UV-UV Hole-Burning Spectroscopy of Protonated Adenine Dimer[END_REF] can be applied to a determined ion in the trap in order to discriminate whether the observed spectral bands belong to a unique species (different transitions sharing the same ground state) or originate from different conformers (further details in the Supporting Information file).

Ab-initio calculations were performed using the TURBOMOLE package, [START_REF] Ahlrichs | Electronic Structure Calculations on Workstation Computers: The Program System Turbomole[END_REF] following the resolution-of-the-identity (RI) approximation to calculate the electron repulsion integrals.

The ground state (S 0 ) geometries of QH + and iQH + were optimized at the MP2/cc-pVDZ level (second order Møller-Plesset perturbation theory, with the correlation-consistent polarized valence double-zeta basis set). Vertical transitions energies and oscillator strengths of the lowest excited singlet states (S 1-3 ) were calculated using the RI-ADC(2) (second order Algebraic Diagrammatic Construction) method, [START_REF] Trofimov | Electron Excitation Energies Using a Consistent Third-Order Propagator Approach: Comparison with Full Configuration interaction and Coupled Cluster Results[END_REF] which was previously found to reproduce adequately the electronic excitations of other ionic systems containing aromatic nitrogen atoms, [START_REF] Noble | The Electronic Spectra of Protonated PANH Molecules[END_REF][START_REF] Taccone | Communication: UV Photoionization of Cytosine Catalyzed by Ag +[END_REF][START_REF] Féraud | Excited States of Proton-Bound DNA/RNA Base Homodimers: Pyrimidines[END_REF] as well as protonated aromatic molecules having nitrogen functional groups. [START_REF] Féraud | UV Spectroscopy of Cold Ions as a Probe of the Protonation Site[END_REF] Computations were performed in C 1 and Cs point-group symmetries. Under Cssymmetry restriction, the S 1 excited states of QH + and iQH + are found of the A'(*) type. Supplementary excited state optimizations starting from non-planar structures returned back to the planar geometry. Ground and excited state zero-point energies (ZPEs) have been calculated for the two protonated quinolines to correct the computed transition energy values.

The vibrational frequencies associated to the ground and the excited states of the QH + and iQH + ions have been calculated to help us assign the experimental vibronic bands. Mulliken notation was used to label the calculated normal modes.

Results:

3.1 Electronic spectra of QH +

In Figure 1 it is presented the difference TOF mass spectra obtained by subtraction of the ion signal corresponding to post-and pre-photodissociation of the parent ion QH + (m/q = 130, negative peak) at fragmentation energies corresponding to h= 42230 cm 1 (236.8 nm) and h= 27871 cm 1 (358.8 nm). According to the observation of Hansen et al., [START_REF] Hansen | Ultraviolet Photodissociation Action Spectroscopy of Gas-Phase Protonated Quinoline and Isoquinoline Cations[END_REF] the most significant signals (positive peaks) found in the photofragmentation mass spectra for an excitation energy between 41600-43500 cm 1 (230-240 nm), at room temperature, correspond to m/q = 77 ions (phenyl cations), formed by either loss of acetylene and hydrogen cyanide molecules or loss of C 3 H 3 N (acrylonitrile or azete), and a smaller yield of m/q = 102 ions, resulting from elimination of 28 mass units given by loss of acetylene + H 2 or CN + H 2 .

If the fragmentation energy is decreased to wavelengths in the spectral region of 27800-29400 cm 1 (340-360 nm), and hence the dissociation process evolves in a different excited state, a drastic change in the branching ratio is observed in the mass spectrum, again in agreement with reference 24. Under such conditions the most abundant fragment observed is the m/q = 103 ion, generated from loss of a hydrogen cyanide molecule, together with two additional minor fragments: m/q = 128 (loss of H 2 or two hydrogen atoms) and m/q = 77 (phenyl ions).

A similar change in the fragmentation pattern is found when QH + is studied by collision induced dissociation (CID) mass spectrometry on going from collision energies of about 50 eV (main fragment, m/q = 77) to 30 eV (main fragment, m/q = 103). [START_REF] Horai | A Public Repository for Sharing Mass Spectral Data for Life Sciences[END_REF] The photodissociation electronic spectra of cold QH + measured by collecting the fragment ion signal on mass channels m/q = 77, 102, 103 and 128 are plotted in Figure 2. The onset of the absorption is more clearly visualized on the m/q = 103 and 128 channels associated to the fragment ions that dominate the mass spectrum upon excitation at lower energy. Three band systems are identified in the spectra. The first band evidences a clear 00 transition at h = 27868 cm 1 followed by a well-defined vibrational structure, where the bandwidths are found only slightly broader (15 cm 1 ) than the spectral resolution of the laser, which should correspond to the convolution of the laser width with the rotational contour. A second absorption appears quite unresolved starting at 32500 cm 1 , which is more clearly distinguished on the m/q = 77 and 102 channels. From the onset of this band it is possible to estimate a transition energy in the range 32000-33000 cm 1 , which agrees perfectly well with the second excited state (S 2 ) energy calculated for QH + (see Table 1). The third transition comes into view at h = 42230 cm 1 , preferentially leading to phenyl fragments (m/q = 77). It exhibits a rather intense 00 transition together with several active vibrational modes. In this third electronic state, however, the bandwidths are markedly larger than those associated with the first excited state (FWHMs  30 cm 1 ). An interesting feature in the photodissociation spectrum of QH + is the closing of the fragmentation channel corresponding to the elimination of hydrogen cyanide above h = 33600 cm 1 , as observed in the spectrum recorded in the m/q = 103 fragment (Figure 2). 30000 35000 40000 45000

m/q = 77 m/q = 102
Intensity (arb.units)

m/q = 103 m/q = 128 excitation energy (cm -1
)

The assignment of the vibrational structure of the first and third absorption bands is shown in Figure 3 by zooming respectively the spectral region in the vicinity of S 1 S 0 and S 3 S 0 transition origins. The active vibrations were labeled using the index of the calculated normal mode that better matches the experimental energy (see Table 2). The S 1 S 0 spectrum of QH + is vibrationally well resolved, having a more complex structure than expected from and 128. Three band systems are observed: i) structured band system starting at h = 27868 cm 1 (with decreasing intensities in mass channels m/q = 103, 128 and 77), ii) unresolved band starting at 32500 cm 1 (better distinguished on the m/q = 77 and 102 channels), and iii) structured band system starting at h = 42230 cm 1 (m/q = 77 and 102 channels).

the photodissociation action spectrum measured at room temperature. [START_REF] Féraud | Development of Ultraviolet-Ultraviolet Hole-Burning Spectroscopy for Cold Gas-Phase Ions[END_REF] It is dominated by three active modes observed at 481 cm 1 (1 and 2 quanta, assigned to 32 ), 492 cm 1 (1 to 4 quanta, assigned to 31 ) and 576 cm 1 (1 to 3 quanta, assigned to 30 ), as well as several of their combination bands. The modes 33 , 29 and 28 are also visible in the spectrum and are excited in combination with some of the other active modes. Even though the S 3 S 0 vibrations are notably broader, we were able to assign vibrational progressions of modes observed at 31 = 480 cm 1 (1-2 quanta), 30 = 578 cm 1 (1-3 quanta) and 29 = 719 cm 1 (1-2 quanta), as well as combination bands involving these modes.

(m/q = 103)

(30 + n 31) (30)
Intensity (arb.units) (31) (m/q = 77)

S 1 S 0 0 1 3 2 0 1 2 (29)
(2 47) Vibronic assignment of the active modes in the spectra was done with the help of S 1 and S 3 calculated normal modes (see Table 2).

2 1 0 ( + n) 3 2 1 0 ( + n) ( + n) (29)

Electronic spectra of iQH +

In agreement with the experiment performed by Hansen et al., [START_REF] Hansen | Ultraviolet Photodissociation Action Spectroscopy of Gas-Phase Protonated Quinoline and Isoquinoline Cations[END_REF] photodissociation mass spectra of trapped QH + and iQH + protonated ions are very much alike, leading to the same fragmentation pattern. For protonated isoquinoline, the main fragment observed via excitation in the 41670-43480 cm 1 energy region is again the phenyl cation (m/q = 77), changing the branching ratio in favor of the hydrogen cyanide loss upon excitation in the 27780-29410 cm 1 region with the consequent predominance of m/q = 103 fragments in the mass spectrum. The same behavior is found in CID mass spectra of iQH + for collision energies increasing from 30 to 50 eV, where the most intense fragment peak changes from m/q = 103 to m/q = 77. [START_REF] Horai | A Public Repository for Sharing Mass Spectral Data for Life Sciences[END_REF] The UV-vis absorption of cold iQH + is given in Figure 4 for the mass channels m/q = 77, 102, 103 and 128. At first sight, the electronic spectrum looks very similar to that of QH + and the band origins almost coincide. At low energies, the band recorded on the m/q = 103 mass channel exhibits a strong 00 transition at h = 28043 cm 1 (356.6 nm) while at higher energies a new band starts at h = 41988 cm 1 (238.2 nm) on the m/q = 77 channel. Similarly to the QH + case, an intermediate unresolved band appears in the m/q = 77 channel, this time at 35100 cm 1 , which compares well with the second excited state (S 2 ) energy calculated for iQH + (see Table 1) and is shifted by ~2500 cm 1 with respect to the QH + second excited state. Just as in the case of QH + , the fragmentation channel leading to the elimination of hydrogen cyanide (m/q = 103 mass channel in Figure 4) closes above 33600 cm 1 for iQH + . 30000 35000 40000 45000

m/q = 77 m/q = 102 Intensity (arb.units)

m/q = 103 m/q = 128 excitation energy (cm -1

)

The first absorption band (S 1 S 0 transition) of iQH + shown in Figure 5 exhibits a well-defined vibrational structure with bandwidths of FWHMs  15 cm 1 , again slightly broader than the spectral resolution of the laser, which should correspond to the convolution of the laser width with the rotational contour. It is possible to distinguish two dominant modes at 31 = 492 cm 1 (1-3 quanta), and 30 = 589 cm 1 (1-2 quanta), and combination bands between them and including the modes 33 and 32 as well. Bands corresponding to the modes 33 , 32 , 29 and 28 have also been assigned in the spectrum. In the same figure it is observed that the vibrational bands linked to the S 3 S 0 electronic transition are markedly broader (FWHMs  130 cm 1 ), which implies that the lifetime of this excited state (S 3 in our calculations) is limited to less than 260 fs, in contrast to the S 1 case. In spite of the large measured by collecting the ion signal on mass channels m/q = 77, 102, 103 and 128. Three band systems are observed: i) structured band system at h = 28043 cm 1 (clearly observed on the m/q = 103 mass channel and more weakly for m/q = 77), ii) unresolved band starting at 35100 cm 1 (better distinguished on the m/q = 77 and 102 channels), and iii) structured band system at h = 41988 cm 1 (m/q = 77 and 102 channels). bandwidths, we have tentatively assigned two vibrational modes (1-3 quanta) at 32 = 461 cm 1 and 30 = 599 cm 1 . 0 500 1000 1500 2000

(31+ 32) (28)

Calculations

The protonation site of QH + and iQH + is limited in our calculations to the N heteroatom (see Scheme 1). The other tautomers with protonation on a carbon atom are at least 12100 cm 1 (1.5 eV) higher in energy according to our calculations. It is worth to remark that high-energy tautomers cannot usually be ignored since they have been occasionally evidenced [START_REF] Alata | Electronic Spectra of the Protonated Indole Chromophore in the Gas Phase[END_REF][START_REF] Féraud | Excited States of Proton-Bound DNA/RNA Base Homodimers: Pyrimidines[END_REF] despite the low temperatures achieved in the trap. In the present case, Cprotonated tautomers were not taken into account based on the results of double resonance experiments (see Supporting Information), which show that only a single species (Nprotonated tautomer) is responsible for the observed spectra. Vibronic assignment of the active modes in the spectra was done with the help of S 1 and S 3 calculated normal modes (see Table 3).

The optimized (MP2/cc-pVDZ) ground state of protonated isoquinoline is 72 cm 1 (0.009 eV) more stable than that of protonated quinoline. C 1 point-group symmetry ADC(2) adiabatic transition energies corrected by the variation of the ZPEs between the excited and the ground states, (E o ), and the respective oscillator strength values (f) are presented in Table 1 for both ions. Important differences are found between vertical (not shown in Table 1) and adiabatic transition energies, reaching 3600 and 2600 cm 1 (0.45 eV and 0.32 eV ) for the corresponding S 1 S 0 transition in QH + and iQH + , respectively. It points out the necessity of performing excited-state optimizations for these molecular ions in order to properly compare the experimental results with the calculations. It is observed in Table 1 that the ADC(2) energy values computed in the present work are in better correspondence with the experimental band onsets (E exp ) than the DFT calculations performed previously, [START_REF] Hansen | Ultraviolet Photodissociation Action Spectroscopy of Gas-Phase Protonated Quinoline and Isoquinoline Cations[END_REF] included in the table between brackets. The energetics of the low lying excited states of QH + and iQH + is very similar, in agreement with the good correspondence between their electronic spectra in Figures 2 and4.

QH + iQH + E 0 /cm 1 E exp/ cm 1 f E 0 /cm 1 E exp / cm 1 f S 1 27
In both molecular ions the excitation to the first excited state (S 1 ) involves a π-HOMO to an antibonding π*-LUMO transition with a moderate oscillator strength, which can be perfectly assigned to the first band of the electronic spectrum (band onsets at 27868 cm 1 for QH + and 28043 cm 1 for iQH + ). In the case of QH + , the next excitation (S 2 S 0 ) can largely be attributed to a (LUMO←HOMO1) transition, for which the magnitude of the oscillator strength is significant. However, the iQH + S 2 S 0 transition involves additional molecular orbitals (HOMO and LUMO+1) and the calculations predict almost no absorption for this transition. This is in agreement with the experiments (m/q = 77 and 102 channels), in which a well-defined band starts at 32500 cm 1 for QH + , very close to the E 0 value calculated for S 2 , while only a very weak absorption at 35100 cm 1 appears in the case of iQH. Supplementary S 1 and S 3 low lying vibrational modes ( calc ) calculated for QH + and iQH + are shown in Tables 2 and3, respectively. The assignment of the experimental bands ( exp ) is done under

the assumption that at the low temperature of the experiment the vibrational modes of the electronic ground state are not excited. We have restricted the list to frequencies lower than 1000 cm 1 and excluded a few unassigned experimental bands of weak intensity. Although most of calculated frequencies agree well with the measured values, in a few cases the assignment must be considered as tentative because  exp  calc  exceeds the experimental resolution of the apparatus (indicated with asterisks in the tables. The calculated in-plane vibrational modes 28-33 are active in the S 1 excited state of QH + under our experimental conditions, three of them being clearly assigned to intense spectral bands: exp = 576 cm 1 ( 30 , nonsymmetrical ring deformation), exp = 492 cm 1 ( 31 , symmetrical breathing), and exp = 481 cm 1 ( 32 , nonsymmetrical ring deformation). The modes 30 and 31 are also active in the S 3 excited state at slightly different frequencies (578 and 480 cm 1 , respectively). The low energy out-of-plane mode 47 is apparently active in the S 3 state of QH + (two quanta match the band at exp = 220 cm 1 ). The in-plane low frequency vibrations calculated for iQH + do not differ much in energy from those of its structural isomer. In-plane iQH + vibrational modes 28-33 are again active in S 1 , the same three modes, exp = 588 cm 1 ( 30 , symmetrical ring deformation), exp = 486 cm 1 ( 31 , symmetrical breathing) and exp = 467 cm 1 ( 32 , nonsymmetrical breathing) prevailing. The modes 30-32 appear to be active in the S 3 excited state of iQH + ( 30 at 656 cm 1 and a band comprising 32 and 31 at 456 cm 1 ), although the assignment is not conclusive due to the large experimental bandwidths. No out-of-plane modes are visible in the experimental spectra of iQH + .

S1 S0 S3 S0

exp (cm  1 ) calc (cm  1 ) assignment exp (cm  1 ) calc (cm

Discussion

The fragmentation spectra of the molecular ions QH + and iQH + look very similar (compare Figures 2 and4), exhibiting two intense band systems associated with the S 1 S 0 and S 3 S 0 absorptions (UV and deep-UV bands, respectively) in addition to a weak broad structure located in between, which has been assigned to the S 2 S 0 absorption. The UV and deep-UV band origins correspond reasonably well with previous estimations done by action spectrometry at room temperature, [START_REF] Hansen | Ultraviolet Photodissociation Action Spectroscopy of Gas-Phase Protonated Quinoline and Isoquinoline Cations[END_REF] although the low temperature of the ions achieved in our experiments allow us to observe well-defined 00 bands and clear progressions of vibrational bands (Figures 3 and5). In the UV and deep-UV range, the electronic spectra of QH + and iQH + are governed by the excitation of  electrons. All the observed transitions are of * character because protonation transforms the n orbital (lone pair) on the nitrogen atom to a  orbital and the resulting * transitions become too high to be observed. * transitions are also calculated beyond experimental access due to their high energies.

In coincidence with previous DFT calculations, [START_REF] Hansen | Ultraviolet Photodissociation Action Spectroscopy of Gas-Phase Protonated Quinoline and Isoquinoline Cations[END_REF] the RI-ADC(2) method also shows that the S 1 S 0 excitation in both QH + and iQH + can be viewed to a great extent as a transition from the HOMO to the LUMO, while S 2 S 0 and S 3 S 0 excitations involve other orbitals.

The probability density of the HOMO is somewhat larger on the non-protonated ring than on the heterocycle, whereas a more uniform distribution characterizes the LUMO. Consequently, a small degree of charge transfer (CT) is involved in the photoabsorption of quinolinium ions, in contrast to the structurally-akin protonated naphthalene (NphH + ) for which the S 1 S 0 excitation involves a clear transition of one electron from the non-protonated to the protonated aromatic ring. [START_REF] Alata | Effect of Protonation on the Electronic Structure of Aromatic Molecules: NaphthaleneH +[END_REF] The S 1 S 0 band origins of QH + and iQH + reported in Figures 2 and4 are shifted about 0.5 eV to lower energies with respect to the onsets of the * transition (S 2 S 0 , in this case) of quinoline [START_REF] Hiraya | Identification of the Lowest Energy n* States in Gas-Phase Polycyclic Monoazines: Quinoline and Isoquinoline[END_REF] and isoquinoline. [START_REF] Hiraya | Multiphoton Ionization Photoelectron Spectroscopy of Molecular Excited States in Supersonic Jet: Low-Lying Electronic States of Isoquinoline[END_REF] The observed spectral shifts to the red denote an enhancement of the proton affinity in the S 1 state, which is probably a common feature among polyaromatic hydrocarbons and N-heterocycles.

An interesting observation comes out when the computed adiabatic excitation energies summarized in Table 1 are compared with the experimental results. Although the ADC(2) transition energies agree very closely with the observed band onsets, the computed oscillator strengths do not reproduce the relative band intensities found in the spectra. For example, one would expect larger f(S 1 S 0 ) values in the calculations for both QH + and iQH + , considering that the experimental bands are very intense. This was also noted previously [START_REF] Hansen | Ultraviolet Photodissociation Action Spectroscopy of Gas-Phase Protonated Quinoline and Isoquinoline Cations[END_REF] for the same species. An explanation for that might be that the oscillator strength effect on the band intensity can be to a great extent compensated by large Franck Condon factors.

The structural similarity of QH + , iQH + and NphH + can also be accounted for by plotting the vibrationally resolved photofragmentation spectra of these ions in the vicinity of the S 1 S 0 band origin, as shown in Figure 6. The low lying active vibrational modes The transition to the S 2 state is observed broad and featureless in QH + and iQH + spectra, probably because it is involved in a fast internal conversion process. However, according to our ab-initio calculations, the excited state S 2 does not lose its planar symmetry and this makes improbable that an out-of-plane non-radiative deactivation channel towards the ground state will take place. The reason for the absence of structure is not clear.

The S 3 S 0 absorption in quinolinium ions is found practically selective to the fragmentation channel leading to the phenyl cation (m/q = 77) and it exhibits a fast deactivation rate estimated in terms of the experimental bandwidths (particularly for iQH + ), which are much larger than the apparatus resolution. A question arises whether the photoexcitation to the S 3 excited state induces the production of phenyl cations by secondary fragmentation of m/q = 103 ions or alternatively a non-sequential fragmentation pathway takes place. Evidence supporting that the phenyl cation is not the daughter ion from the m/q = 103 fragment arises by considering the different rate of formation of both ions. It was found that while the phenyl fragments are produced in a very short time (less than 100 ns) after the fragmentation laser pulse, it takes several milliseconds for m/q = 103 fragments to appear in the trap.

The ultrashort lifetime of the S 3 excited state suggested by the bandwidths appearing in the deep-UV absorption of iQH + and, to a lower extent, QH + might originate from a nonradiative deactivation via isomerization processes like those occurring in other azabenzenes.

For example, valence isomers such as Dewar and prefulvene structures have been proposed as intermediates associated to the 2-3 ps relaxation of the lowest * excited state measured for isolated pyridine [START_REF] Zhong | Femtosecond dynamics of valence-bond isomers of azines: transition states and conical intersections[END_REF] and for protonated pyridine in solution [START_REF] Chachisvilis | Femtosecond Dynamics of Pyridine in the Condensed Phase: Valence Isomerization by Conical Intersections[END_REF] by femtosecond time-resolved mass spectrometry and transient absorption, respectively. A conical intersection located by ab-initio calculations of the potential surfaces was found to play a determinant role in the isomerization pathway leading to the ultrafast deactivation. [START_REF] Srinivasan | Dark Structures in Molecular Radiationless Transitions Determined by Ultrafast Diffraction[END_REF] Dewar pyridines have also been produced by argon matrix isolation and UV irradiation and characterized by FT IR. 39 Although the Dewar forms of protonated quinoline and isoquinoline are energetically accessible from their S 3 excited state according to DFT/B3LYP calculations, no direct evidence on the formation of these photoisomers is derived from our experiments.

Finally, photoproducts and branching ratios do not change from QH + to iQH + and are consistent with those obtained by action spectroscopy at room temperature, which were extensively analyzed in reference 24.

Conclusions

The key result of the present work is the presentation of cold photofragmentation spectra of single-isomeric protonated quinoline and isoquinoline ions, together with ab-initio adiabatic transitions energies that nicely match with the experimentally well-defined band onsets. Although the second band in the electronic spectra does not show any vibrational structure, the first and the third absorptions show several in-plane vibrations that have been analyzed and assigned with the help of calculations performed in the ground and the excited states.

The bandwidths measured in the deep-UV absorption of iQH + and, to a lower extent, in QH + denote that the lifetime of the S 3 excited state is in the subpicosecond time scale, possibly via a relaxation pathway involving valence photoisomers.

Scheme 1 .

 1 Scheme 1. Left, protonated quinoline (quinolinium ion, QH + ); right, protonated isoquinoline (isoquinolinium ion, iQH + ).

Figure 1 .

 1 Figure 1. Difference (photodissociation laser: on  off) TOF mass spectra of protonated quinoline (m/q = 130, negative peak) at h= 42230 and 27870 cm 1 . Ion fragment signals (positive peaks) at m/q = 77 (phenyl cation), 102, 103 and 128 result respectively from loss of HCN+C 2 H 2 (or C 3 H 3 N), C 2 H 2 +H 2 (or CN+H 2 ), HCN and H 2 .

Figure 2 .

 2 Figure 2. Photofragmentation electronic spectra of protonated quinoline measured by collecting the ion signal on mass channels m/q = 77, 102, 103

Figure 3 .

 3 Figure 3. Photofragmentation spectra of cold protonated quinoline in the vicinity of the first (S 1 S o ) and third (S 3 S o ) band origins. The spectra were recorded with a 0.02 nm scanning step on the indicated mass channels.

Figure 4 .

 4 Figure 4. Photofragmentation electronic spectra of protonated isoquinoline

Figure 5 .

 5 Figure 5. Photofragmentation spectra of cold protonated isoquinoline in the vicinity of the first (S 1 S o ) and third (S 3 S o ) band origins. The spectra were recorded with a 0.02 nm scanning step on the indicated mass channels.

S

  1 and S 2 optimizations have been performed starting from non-planar structures, which converged back to planar geometry. The third excitation (S 3 S 0 ) computed for QH + and iQH + lies in the deep UV region, showing E 0 values close to the observed band onsets at 42230 cm 1 and 41988 cm 1 , respectively. Even though several molecular orbitals contribute to this transition in iQH + , the (LUMO+1←HOMO) transition prevails. According to our calculations, * states are not energetically accessible. Under Cs-symmetry restriction, the optimized S 1 excited state of QH + and iQH + are found of A'(*) type and the transition energies are the same as with the C 1 symmetry calculation.

Figure 6 .

 6 Figure 6. Comparison among the photofragmentation spectra of protonated quinoline (QH + ), isoquinoline (iQH + ) and naphthalene (NphH + ) in the vicinity of the S 1 S 0 band origin. The numbers label the low lying active vibrational modes.

Finally

  , we have observed that the vibrational progressions in the S 1 excited state of QH + and iQH + look very similar and resemble that of the structurally related protonated naphthalene.Bibliography: 1. I. S.; Larsen, O. F. A.; de Voogt, P.; Gooijer, C.; Velthorst, N. H. Isomer-Specific Detection of Azaarenes in Environmental Samples by Shpol'skii Luminescence Spectroscopy. Anal. Chim. Acta 1997, 354, 181187. 2. Blumer, M.; Dorsey, T.; Sass, J. Azaarenes in Recent Marine Sediments. Science 1977, 195, 283285. 3. Pereira, W. E.; Rostad, C. E.; Garbarino, J. R.; Hult, M. F. Groundwater Contamination by Organic Bases Derived from Coal-Tar Wastes. Environ. Toxicol. Chem. 1983, 2, 283294. 4. Bleeker, E. A.; Wiegman, S.; deVoogt, P.; Kraak, M.; Leslie, H. A.; de Haas, E.; Admiraal, W. Toxicity of Azaarenes. Rev. Environ. Contam. Toxicol.2002, 173, 3983.

Table 1 .

 1 ADC

		370 (29 971)	27 868	0.040 (0.04)	27 810 (29 955)	28 043	0.07 (0.070)
	S 2	32 730 (35 737)	32 500	0.074 (0.097)	34 770 (37 052)	35 100*	0.0007 (0.001)
	S 3	42 730 (46 247)	42 230	0.63 (0.64)	43 420 (46 494)	41 988	0.65 (0.71)

(2) adiabatic excitation energies (E 0 ) for protonated quinoline and isoquinoline (DFT calculations performed in reference 24 are enclosed in brackets) and oscillator strengths (f). Experimental transition energies (E exp ) are taken from band origins; (*) very weak transition, the assignment of the band onset at 35100 cm 1 is tentative. Ground state geometry optimized in C 1 point-group symmetry (MP2/cc-pVDZ).

Table 2 .

 2 Experimental vibrational frequencies and calculated normal modes of QH + for the S 1 S o and S 3 S o transitions. (*) Tentative assignment.

	 1 )	Assignment

Table 3 .

 3 Experimental vibrational frequencies and calculated normal modes of iQH + for the S 1 S o and S 3 S o transitions. (*) Tentative assignment.

  28-33 of QH + and iQH + match reasonably well with the modes 29-34 of NphH + (see supplementary information of reference 27). The first mode in the region of 340 cm 1 (indicated as 33 for the protonated quinolines and 34 for protonated naphthalene) correspond to the in-plane symmetric bending, while the mode at 485 cm 1 ( 31 , QH + and iQH + ; 32 NphH + ) is a symmetric breathing, and the other modes involve different in-plane deformations of the carbon skeleton. The modes 29-31 are also present in the S 3 S 0 excitation.

	QH +	~29 28  : 33 32 31 30
	iQH +	~  : 33	32 31 30	29 28
		~  : 34	33 32 31	30 29
	0		500	1000
			~  (cm -1 )


Alexei Khomiakov

Lev Karsavin

Françoise Lesourd

Université Jean

Moulin Lyon

A Possible Filiation Between

Khomiakov exerted a certain influence on Lev Karsavin, one of the leading Russian philosophers of religion of the twentieth century.

Lev Karsavin was born in Saint Petersburg in 1882

ideology that could take the place of communism after the end of what they expected to be a short-lived Soviet era.

Karsavin had never accepted his émigré status, but was gradually obliged to recognize that the Soviet regime was probably going to remain in place for a considerable time, and was forced to admit that: "we will probably never go back to Russia." Nevertheless, he reframed Eurasianist ideology, which was set out in several pamphlets, in particular: The Foundations of Politics 1 and A Phenomenology of Revolution 2 , in both of which a Slavophile influence can be felt. In fact, the notion of Eurasia was of little importance to him: it was Russia that really interested him.

As he wrote in 1923: "Do they [the Eurasianists] really think that all things 'European' and 'Russian' should be eliminated, and replaced by something that is 'Eurasian' (whatever that might be)?" He goes on: "I am Russian, and I prefer to die along with my Russian fellow countrymen.

It is not in times of trial and tribulation that one should renounce one's language and one's country." 3 However, he endorsed the Eurasianist attempt to re-establish links with the new-Soviet-reality of Russia.

In 1926 he moved to Paris, where the core of the movement was based, but left it after little more than a year, not only because of his disagreements with the "right-wing" Eurasianists, who were unwilling to recognize the Soviet authorities, but also because of the opacity of its funding (it was suspected that the movement was financed in part by the Soviet secret services), and above all because he had been invited to take up the chair of world history at the University of Kaunas, the then capital of newly-independent Lithuania. From 1928 on, his destiny was 1 "Osnovy politiki", Evraziiskij vremennik, V, Paris, 1927, repr. 1992 (Daidžest, Tver). 2 "Fenomenologija revoljucii", Evraziiskij vremennik, V, Paris, 1927, repr. 1992 (Daidžest, Tver)..3 « Evropa i Evrazija », Sovremennye zapiski, Paris, 1923, XV, N°II, p. 298 ("Čto že, oni dumajut, budto pogibnet i «evropejskoe» i «russkoe», i na smenu pridet kakoe-to «evrazijskoe» […] ? Togda mne, russkomu čeloveku, ix evrazijstva ne nadobno, i ja predpočtu pogibnut' so svoim russkim pravoslavnym narodom. I v minutu tjažkix ispytanij mne ne pristalo otkazyvat'sja ot rodnogo jazyka i rodnogo imeni"). linked to that of his Lithuanian university; within a few months he was lecturing in Lithuanian, and it was in this language that he wrote his monumental History of European Culture. 1 At the end of the Second World War, when Lithuania became a Soviet satellite, he was encouraged to leave, as it was dangerous for someone forced into exile in 1922 to find himself in Soviet territory again. But he wished "to be re-united with Russia,"2 and was convinced that the Soviet authorities "had changed"; he therefore decided to stay, but in the course of time, despite his loyal co-operation, he was obliged to give up his position at the university, and was later forced out of his post as director of the Vilnius Museum of Fine Arts. In 1949, he was arrested and incarcerated in the city's prison for a year, during which the first signs of tuberculosis became apparent. He died of the disease in the summer of 1952 in the Abez prison camp (located south of Vorkouta), where he was serving a ten-year sentence 3 .

It was more especially after the revolution that the links between his philosophy and Khomiakov's thinking emerged and the importance of the latter's thought for an understanding of Russia's historical destiny in the twentieth century came to be recognized. But in fact, even in Karsavin's youth, when his attention was particularly focused on Bernard of Clairvaux, Abelard, and Saint Francis, etc., he had already published an article (on the papacy) that demonstrated a certain kinship with Khomiakov4 . Moreover, this closeness was intentional: he claimed (probably wrongly, however) to be related to him through his mother.

This paper, written in 1910, addressed a subject dear to the Slavophiles: the birth of the papacy as an institution and the specificity of the Roman Church. It is a scholarly study, without any obvious polemical intent. But the influence of Khomiakov is clearly perceptible: the "democratic" spirit of the nascent Roman Church is clearly underscored, the "charismata" are seen, at that time, as involving all the faithful, whereas they subsequently went on to become the preserve of the few, the "pastors," whose role, moreover, is justified by the importance of the Eucharist in worship. Furthermore, the choice of the word "pastor" ("presviter") is significant, as it indicates the type of relationship between the faithful and the leaders of the early church, and is a term often used by Khomiakov.

In this article, the influence of Khomiakov is unexpectedly intertwined with that of Vladimir Soloviev. In his treatise, The Great Controversy and Christian Politics,1 the latter author admits that papal authority could be justified by the part played by different Popes-as guardians of Church doctrine in the struggle against heresy-at a dangerous time, that of Marcion, the Gnostics, etc.

After the 1917 revolution, the influence of Khomiakov took on a new dimension, and he came to be seen as the veritable prophet of the Russian catastrophe. Karsavin's pamphlet East, West and the Russian Idea 2 portrays the revolution as a "second period of rampant Westernization" 3 after that of Peter the Great. In this document, Khomiakov's ideas on the Westernization of Russia and its damaging consequences are melded with what is peculiar to Karsavin himself: a particularly profound knowledge of medieval Western spirituality and the concept of a "dualism of religious consciousness" (that is, two contrary orientations: the one directed towards the world and good works, in order to attain salvation, and the other towards contemplation and prayer; the idea of a complete break between God and the world, or that of possible access to the Godhead). This opposition between the two types of spirituality is reminiscent, to a certain extent, of Khomiakov's distinction between what he calls the "Persian" and the "Cushitic" principles 4 , which he, however, used to distinguish between two main types of culture. For Karsavin, it is the type of spirituality that defines the type of culture. His understanding of the notion of "faith" is so broad as to be almost synonymous with the concept of "mentality." From Karsavin's perspective, as can be seen in East, West and the Russian Idea, Russia occupies an intermediate position: for him, its type of religiosity is "Eastern," but he conceives it as belonging within an overall European framework. Both thinkers attach fundamental importance to the question of the filioque. But whereas Khomiakov simply considered the matter as a "crime" perpetrated by the West against its Eastern brothers, Karsavin emphasizes the consequences of this change in dogma upon people's worldview. The insertion of the filioque introduces into the Trinity a sort of second unit, comprising the Father and the Son. It reduces the part played by the Holy Spirit and renders impossible "the manifestation of God within the created world"1 , because of the sharp break thus introduced.

The Russian catastrophe, he continues, is due to the imposition of a foreign, Western, ideal of exclusively earthly happiness, involving "both the refusal of an inaccessible heavenly life, and an ideal of empirical prosperity presented as an absolute," on a country whose religious consciousness was of a different (passive, contemplative) type. Yet Russia, he writes, needs to carry through to its conclusion the trial imposed upon it in order to realize its full potential and truly become itself through the demise of the old world (the old regime). Karsavin's ontology can be summed up, therefore, in the expression: "Life through death." Some time later, however, his closeness to Khomiakov was explicitly manifested when Eurasian Book Publishers in Berlin republished the latter's essay, "The Church is One," with a preface by Karsavin entitled "On the Church."

Judging by the title, one might expect Khomiakov's essay to target Western Christian confessions, considered as heretical, and cut off from the ecumenical Church. On first sight, this in fact seems to be a incorrect impression: Khomiakov speaks of the oneness of the church visible and invisible, and the grace which reaches out to all men, at all times. In Khomiakov's Collected Works, its full title is: "A Catechetical Exposition of the Teaching of the Church." At first sight then, it is simply a catechism. It may appear strange, to Western eyes, that a secular author should write a "catechism." Yet in Russia, on the other hand, it represented a major innovation. I refer readers here to the article by Antonella Cavazza1 , in which she admirably demonstrates the novel character of this initiative (a point of which Westerners would otherwise be unaware). This typically Russian tradition-the elaboration of theology by secular authors-which Karsavin, moreover, went on to continue, may strike us as surprising. But there was none other.

As is well known, the Orthodox Church confined itself exclusively to Holy Scripture and the first seven ecumenical councils. Exegesis was not allowed, and there was no other text. The very first catechism, produced by Peter Mohila in the early eighteenth century, remained largely unknown. That of Metropolitan Philaret appeared shortly before Khomiakov's essay.

Khomiakov set out the fundamental truths of faith in straightforward contemporary language. This corresponded to a pressing need, as certain accounts evince. However, his essay was regarded with suspicion by the religious authorities, who were apprehensive about even a simple presentation of the truths of faith, when produced outside the Church, whereas Khomiakov himself considered that he had helped the Russian Church by filling a gap. For, by refusing to accept a modern formulation of the truths of faith, it was depriving itself of a means of countering the influence of the Western churches.

The essay consists firstly of a systematic presentation of the principal religious truths: religious life is grounded in Holy Scripture, good works, and tradition; their authenticity flows from the person of Christ, who is the foundation of doctrine as a whole; religious truths cannot be rationally demonstrated; the creed, which occupies a central place, sets out mysteries that are inaccessible to reason. Next come the enumeration and explanation of the theological virtues and all the sacraments, and then the essay deals with the Last Judgment, and the Resurrection, just as in an ordinary catechism. It offers an answer to a frequently asked question on the value of the sacraments administered by unworthy priests: the value of such sacraments is not lost as, in each instance, the rite is performed by the whole church.

But in fact, we very quickly discover there is a polemical intention hidden beneath each point dealt with in the presentation. The Church as a unified body possesses the truth, whereas an individual person may fall into error. The Church "cannot acknowledge that any particular private individual or bishop or patriarch or their successors are immune from succumbing to error in doctrine and that they are protected from error by some special grace" 1 . Clearly Khomiakov's target is papal infallibility.

"The Church," writes Khomiakov, "belongs to the whole world, and not any locality" 2

The fact that "Rome" has become the symbol of ecumenism in the minds of some people should not disguise the fact that Rome is no more than an insignificantly small territory on a terrestrial scale. What is accepted by the Church is that which is "proclaimed by a General Council and common agreement" 3 , and not by the will of a single individual (the Pope). In Western cultures, the desire to prove the existence of God is fairly widespread, but this only demonstrates "the pride of reason and unlawful power" 4 .

But the worst sin of all consists in adding to the canonical texts. And this, of course, alludes to the filioque, which introduces a sort of new dogma into the teaching of the church : "…the addition of the word filioque contains some illusory dogma unknown to any of the Godpleased writers, bishops, or apostolic successors in the first centuries of the Church; nor was it spoken by Christ the Savior" 5 . As regards the Eucharist, the Catholic term of "transubstantiation" is not rejected, but the Holy Church "does not ascribe to it the material 1 On spiritual unity, A Slavophile Reader, Ivan Kireevsky, Alexeï Khomiakov, translated and edited by Boris Jakim and Robert Bird, Lindisfarne Books, 1998, p. 33 ; Xomiakov A., Izbrannye sočinenija, N.-Y., Čehov ed., 1955, "Opyt katexizičeskogo izloženija učenija o Cerkvi", p. 210. ("Ona ne možet priznat', čto sie čatnoe lico, ili episkop, ili patriarx, ego preemniki, ne mogli vpast' v ošibku po učeniju i čto oni oxraneny ot zabluždenij kakoj-nibud' osoboj blagodat'ju"). 2 Ibid. ("…ona prinadležit vsemu miru, a ne kakoj-nibud' mestnosti"). 3 Ibid. ("obščim soborom i obščim soglasiem"). 4 Ibid., p. 38 & 214 ("gordost' razuma i nezakonnoj vlasti"). 5 Ibid., p. 38 & 215 ("… pribavlenie slov filioque soderžit kakoj-to mnimyj dogmat, neizvestnyj nikomu iz bogougodnyx pisatelej ili iz episkopov ili apostol'skix preemnikov v pervye veka Cerkvi , ni skazannyj Xristom Spasitelem").

sense attributed to it by the teachers of the churches that have fallen away"1 , as it represents a drift towards magic. Ritual is one of the foundations of the life of the Church, but if the importance attached to it becomes exclusive, it distances man from God: such is the case of the "ritualism" of the Catholic Church. Thus, what might at the outset have appeared to be a simple catechism ultimately turns out to be a polemical essay.

While Karsavin prolongs the tradition of theological elaboration by secular writers, he adds new dimensions, because of the new historical situation. For him-and this is already visible in his earliest historical studies, and even more so towards the end of his life, in his dialogues with Vaneyev-dogma needs to become (or once again become) the object of intellectual attention, in order to respond to the modern-day secularization of culture. Karsavin's introduction to "The Church is one" is a veritable apologia for Khomiakov. It demonstrates the relevance of his thought just as the Bolshevik revolution was confirming the validity of his vision of the evolution of Russian culture, and the impasse into which it had been drawn by one-sided Occidentalism (Karsavin mentions Khomiakov's curious lightheartedness at the time of the siege of Sebastopol). He points out that Khomiakov had practically no readers in Russia, and suggests that it may be for this reason that he wrote his essays in various foreign languages.

Karsavin underscores the fact that Khomiakov neither refused the idea of progress, nor rejected the contribution of Peter the Great, and he cannot be considered to be a chauvinistic nationalist (on the contrary, he never ceased to emphasize the running sores of life in Russia).

Herzen rightly said of the Slavophiles: "The importance of their conception, their truth, and the most essential part of their thinking lies not in Orthodoxy and an exclusive nationalistic mindset, but in those elements of Russian life that they have helped to reveal beneath the silt of an artificial civilization" 1 . These particular "elements" [stihii] has very little to do with the "people," which is a notion invented by the intelligentsia (the "ruling layer of society" which has lost its "organic character," as Karsavin points out in A Phenomenology of Revolution 2 ).

What gives particular relevance to Khomiakov's ideas is the fact that the end of the First World War revealed the bankruptcy of European values, all across Europe, but more especially in Russia. Indeed, it was precisely because of the catastrophe of the revolution that the country became involved in the common destiny of Europe. It was at this time that certain Russian intellectuals turned away from Europe, and began to look "towards the East." Not so Karsavin, who stressed that, despite everything, Russia is inconceivable outside Europe as a whole.

Karsavin's preface demonstrates not only common thinking with Khomiakov, but also a kinship of sensibility: the latter warns against an abstract understanding of Christianity ("it is not without the body that we shall be resurrected" 3 ). Incarnation is the core of the Christian idea, Karsavin underlines, and abstraction is harmful. During this period he even wrote an article entitled: "On the Dangers of Abstract Christianity and How to Overcome It" 4 . More importantly, his attitude towards emigration can also be explained in part by his refusal of abstraction, highlighting a new aspect of the Westernization of Russia, the loss of the concrete:

"what is foreign is only concrete in its place of origin, and is only assimilated in an abstract form" 5 .

The idea of the Church is inseparable from Khomiakov's idea of sobornost, but the latter concept takes us well beyond ecclesial life stricto sensu. It is an idea that is very close to Karsavin's 1 Herzen A., Soč. v 9 tomax, M., 1956, t. 5, Byloe i Dumy, IV, chap. 30, p. 133 ("Važnost' ix vozzrenija, ego istina i suščestvennaja čast' vovse ne v pravoslavii i ne v isključitel'noj narodnosti, a v tex stixijax russkoj žizni, kotorye oni otkryli pod udobreniem iskusstvennoj civilizacii"). 2 Karsavin L. P., Fenomenologija revoljucii, op. cit., p. 19 ("pravjaščij sloj", kotoryj "utračivaet svoj organičeskij xarakter"). 3 On spiritual unity, A Slavophile Reader…, op. cit., p. 42 ; "Opyt katexizičeskogo izloženija učenija o Cerkvi", op. cit., (« ne bez tela voskresnem »), p. 218. 4 « Ob opasnostjax i preodolenii otvlečennogo xristianstva », Put ', Paris, 1927, N°6, p. 32-49;repr. Malye sočinenija, SPb., Aleteja, 1994, p. 395-413. 5 Fenomenologija revoljucii, op. cit., p. 17 (« Ved' čužoe konkretno liš' u sebja na rodine i osvaivaetsja tol'ko v abstraktnoj forme ») Orthodox authorities regarded him with suspicion (Semyon Frank wrote of him in a letter that he enjoyed "sowing the seeds of heresy").

On this point, perhaps what was most characteristic of him was his correspondence with Father Wetter. When Gustav Wetter first contacted Karsavin, he was a youthful Jesuit priest planning to write a dissertation on the Orthodox conception of the Trinity. They very soon began discussing the subjects closest to their hearts. Their correspondence1 offers a unique example of a particularly intense inter-faith dialogue on topics of Christian metaphysics. Initially, Karsavin stated that he had always been "at war" with Catholicism (which is rather surprising when one thinks of his early work, his edition of Angela of Foligno's mystical illuminations in The Revelation of the Blessed Angela, or his treatise on Catholicism). But at the same time he wrote to Father Wetter: "Catholicism differs from Orthodoxy in that it is a rigorously and precisely formulated system that sets out the limits to individual philosophical reflection. But the metaphysics that I myself defend does not, I fear, fit entirely within the framework of traditional Orthodoxy."2 This, then, is where Karsavin's profound kinship with Khomiakov lies; for him, true dialogue is not so much compromise as a deepening of the understanding of one's differences as part of an authentic quest for truth.

Europos kultūros istorija, Humanitarinių mokslų fakulteto Raštai, Kaunas, V. D. Universiteto Humanitarinių mokslųfakultetas, 1931-1936, repr. Vilnius, Vaga, 1991.

Unpublished letter to Elena Skržinskaja, Lietuvos Ypatingasis Archivas, P. 11972 LI, n°16416.

Vaneev A. A., «Dva goda v Abezi», Minuvšee, N°6, М., 1992.

«Rimskaja cerkov' i papstvo do poloviny II veka »(Žurnal Ministerstva Narodnogo Prosveščenija, XXX, nov. 1910, N°11).

Solov'ev Vl., Velikij spor i xristianskaja politika, 1883 (Sobr. soč., SPb., izd. Prosveščenie, 1911-1914, t. IV).

Vostok, zapad i russkaja ideja, Pg., 1922. Repr. : Jastrebitskaja A. L., Istorik-medievist -Lev Platonovitch Karsavin, M., INION, 1991.

Ibid., p. 105 (« vtoroj ostryj krizis evropejzacii »).

Especially in his Zapiski o vsemirnoj istorii, published for the first time in 1860 (in the review Russkaja Beseda).

Vostok, zapad i russkaja ideja, op. cit., p. 108 ("javlenie božestva v tvarnom").

Cavazza A., « Sur les sources de l'essai d'A. S. Khomiakov "L'Église est une" », Slavica Occitania, Toulouse, 41,

2015, p. 177-189.

Ibid., p. 42 &

("Ne otvergaet ona i slova presuščestvlenie, no ne pripisyvaet emu togo veščestvennogo smysla, kotoryj pripisan emu učiteljami otpadšix cerkvej") .

« ontologičeski neobxodimaja smert' », Filosofija istorii,Berlin, Obelisk, 1923, repr. SPb., Komplekt, 1993, p. 80.

Perepiska A. Vettera s L. Karsavinym, Simvol, N°31, Paris, 1994, p. 104-169.

Ibid., p. 109 (« …katoličestvo otličaetsja ot pravoslavija kak raz tem, čto javljaetsja strogo i točno vyražennoju sistemoju, kotoraja stavit grani umstvennomu filosofstvovaniju. Mnoju že zaščiščaemaja metafizika, bojus', ne vpolne umeščaetsja i v ramkax tradicionnogo pravoslavija").

idea of the "symphonic person," and is linked to his very individual ontology, which comes from Nicholas of Cusa (and his est/possest distinction) and Hegel.

The concept of the symphonic person can be briefly summed up as follows: all reality is made up of a multiplicity of collective (symphonic) persons. These represent a sum of potentialities and hence are in retraction. At a given point in time, one of these potentialities separates from this sum of elements in retraction, undergoes a transition from a state of potentiality to one of reality, and is individuated, acquiring certain precise concrete qualities ("kačestvovanie"). Some time later it is, as it were, annihilated: it then goes back towards the center and resumes its status of potentiality. But it does not disappear entirely and can later be realized once more as a new, concrete, individual realization of the higher symphonic person: in sum, a sort of metaphysics of the circle. Its center brings together, in a reduced concentrated form, all the potentialities, and its circumference is made up of the infinite number of their possible realizations. This conception is reminiscent of the well-known Renaissance representation of God: a sphere whose center is everywhere and whose circumference is nowhere.

The fact that, sooner or later, the person comes back to the center is what Karsavin calls "ontologically necessary death" 1 . But the person in question may also voluntarily give up his individuality for the benefit of others: hence self-sacrifice lies at the center of this fundamentally Christian conception. The complete realization of one's "self" supposes a willing acceptance of death, on behalf of another (a fellow being, or a higher "symphonic person").

In this interpretation, Khomiakov's sobornost acquires new, darker characteristics, but at the same time it becomes an organic component of an overall world vision and a whole conception of existence. It is complemented by a philosophy of self-sacrifice that also impinges on the political domain. The type of society to which Karsavin aspires, and which he defines in his writings on Eurasianism, supposes on the part of each individual "constant live communication with other like persons" 1 . Communication between people involves self-denial, indeed this is even its main feature (as can be seen, in particular, in his Poem of Death). As he writes in The Foundations of Politics: "At the root of communication between people lies love, once again empirically expressed by the idea of service for the individual and collective benefit of others, which is ontologically equivalent to the mutual gift of self" 2 .

Orthodoxy is particularly well suited to expressing the Christian idea of self-denial, because it is unaffected by the filioque heresy, and has kept the primitive tradition intact. It encapsulates Russia's past and its future. But Karsavin's reflections on the essence of Orthodoxy were accompanied by very real pain at the risks to the Russian Orthodox Church during the Soviet era. As the threat to the Russian Orthodox Church increased and the prospect of his being able to return to Russia receded even further, his articles became increasingly polemical. This was doubtless coherent with the spirit of Khomiakov's thinking, but at the same time the polemical aspect of both authors' writings went together-surprisingly-with a desire for dialogue. Khomiakov's son, Dmitri, once wrote to André Gratieux, the author of a dissertation on his father 3 : "Essentially, nothing is more harmful to a desirable union than when both parties are unable to clearly recognize the differences that separate them; and for this reason, I have always considered my father's theological writings to be not so much polemical as 'irenical,' because in their author's mind their-positive-aim was to clarify respective positions, and not to crush his adversaries." 4 The same can be said of Karsavin, only more so: his religious positions are hard to define clearly. He was considered to be a staunch defender of Orthodoxy and an enemy of Catholicism (in Lithuania, he had only been very reluctantly accepted by the Catholic hierarchy), yet the 1 Osnovy politiki, op. cit., p. 24 (« postojannogo i živogo vzaimoobščenija s drugimi takimi že ličnostjami »). 2 Ibid., p. 25 (« V osnove že vzaimoobščenija ležit ljubov', èmpiričeski vyražaemaja ešče ideeju služenija drugim i celomu, ontologičeski tožestvennaja vzaimootdače »). 3 Gratieux A., A. S. Khomiakov et le mouvement slavophile, Paris, Cerf, 1939. 4 Dmitri Xomiakov's letter (in french) to André Gratieux, in : Gratieux A., Le Mouvement slavophile à la veille de la révolution, Paris, Cerf, 1953, p. 60 (« Rien n'est au fond plus nuisible pour une union désirable que quand les deux partis ne se rendent pas nettement compte de ce qui les sépare ; et pour cette raison j'ai toujours regardé les écrits théologiques de mon père comme beaucoup moins polémiques qu'"iréniques", parce qu'ils avaient dans l'esprit de l'auteur le but positif d'éclaircir la situation réciproque, et non celui de pourfendre les adversaires »).


Y Lefèvre

M Lajofo-Mazenc

E Sarraute

H Camon

First steps towards design, simulation, modelling and fabrication of electrostatic micromotors

Keywords:

Following the principles proposed by workers at Berkeley University, we have developed a version of the electrostatic micromotor based on the sacrificial layer method combined with oxidation of the rotor. In_ ord_ er to study the behaviour of this electrostatic micromotor, we have elaborated Iwo softwares. The first, called EFCREL, is to sjmulate the static operation of the electrostatic micromotors and the second, called EFDYN, is to simulate their dynamic oper;i.tion. Both are based on a finite-element code, called EFCAD, for electromagnetic field computation. They help us with the design of the fabricated micromotor and the simulation of its dynamic working, respectively. The elaboration of these two softwares represents our first steps towards a fully integrated CAD (computer aided design) system for microrriotor � .

Introduction

The principles of design, fabrication and operation of electric micromotors have been investigated in recent years [START_REF] Lang | Towarcl the design of succcssful clcctric micromotors[END_REF][START_REF] Bart | Elcctric micromotor dynamics[END_REF]. This paper discusses our experience of related issues.

Before manufacturing a micromotor, we have to design it. The design procedure has several stages. At each stage design tools are needed, for example: op timization of the main dimensions, optimization of the electromechanical structure, mask design, semiconduc tor process simulation, mechanical structure and ma terials modelling. The final goal is a CAD (computer aided design) integration that involves a continuous computerized chain from the design to the finished product, but this is difficult to achieve. Currently various CAD tools are used independently of one another.

This paper describes our first steps towards the design of a micromotor and is devoted to electromechanical modelling and design that can be implemented in a CAD procedure. Two CAD tools are presented. One is devoted to the design of the electromechanical struc ture and the other is devoted to the design of the electric or electronic supply. Both are linked to an electric field computation code. The first one, described in Section 2, is based on a simulation procedure of the static behaviour of an electric micromotor. It helps us to design an electrostatic micromotor. This micro motor has been fabricated and a brief description is given. Section 3 describes the second tool, which is based on a simulation of the dynamic behaviour of an electric motor. This second tool is applied to the study of the dynamic behaviour of the micromotor.

Simulation of the static behaviour

Preliminary design using simple analytical expressions of the main electromechanical quantities, such as torque and flux, gives roughly the main dimensions of the machine (air-gap value, radius of the rotor, etc.). Then other parameters like the number of electrodes, the number of poles and the shape of electrodes must be determined. To make the optimum choice, designers must study for eacb set of these parameters the per formance of the motor under design. At this stage of the design procedure, electromechanical quantities that characterize its electromechanical behaviour must be defined. Analogies from the classical magnetic electrical motor can be useful. The comparison between electric field and magnetic field formulations in a 2D finite element code has been studied [START_REF] Sarraute | Méthodes de calcul du champ électrostatique appliquées à la simulation de micromotcurs li capacités variables[END_REF]. The results of this study show that with minor changes, a 2D finite-element code devoted to classical magnetic machines can be used. These codes have been much improved and are very well adapted to the analysis of electrical machines. In particular,. we have used methods that allow the characteristic quantities to be calculated taking into account the movement of the rotor [START_REF] Saclowski | Finite elcmcnt torque calculntion in clectrical machines while con sidering the movcment[END_REF]. For an electric motor these quantities are the electric driving torque, the coefficients of capacitance of each electrode and the coefficients of induction between two electrodes. These quantities are qualified as static because they are computed as a function of the rotor position. Modules that can calculate these quantities have been implemented in a 2D finite-element code called EFCAD [START_REF] Sarraute | Méthodes de calcul du champ électrostatique appliquées à la simulation de micromotcurs li capacités variables[END_REF] .

For example, the static operation of an electric mi cromotor bas been simulated. Fig. 1 shows the scalar equipotential lines in the micromotor when only one phase of the stator is supplied. Fig. 2 shows the electric driving torque versus rotor position due to two phases. Many other electrical structures of micromotor have been simulated [START_REF] Sarraute | Etude et modélisation de microactionncurs intégrés sur silicium[END_REF]. The results obtained allow us to choose a motor design. This micromotor, which is shown in Fig. 3, is a three-phase radial-gap variable-capacitance motor with a stator poles number to rotor pales number ratio of 3/1. The geometrical dimensions are 120 µm diameter, 4 µm air gap and 1.5 µm thickness. The number of rotor poles is six with an angular width of 18 ° and an angular pitch of 60 °. The stator pole angular width is 16 ° with 4 ° separation between the stator pales.

Following the principles proposed by workers at Berkeley University, the fabrication is based on the surface micromachining technique, which means a pro cess for depositing and etching multiple layers of sac rificial and structural thin films to build complex mi crostructures [START_REF] Fan | IC-proccssed clcctrostatic micromotors[END_REF][START_REF] Fan | IC-processed clectrostatic synchronous micromotors[END_REF]. The material set from which the micromotor is fabricated consists of four basic elements: polycrystalline silicon doped with phosphorus, which serves as the conducting material, silicon nitride, which serves as the insulating structural materîal, silicon oxide, which serves as an insulating layer as wcll as a sacrificial layer and spin on glass (SOG), which only serves as a sacrificial layer. At this stage, the technological process bas been carried out successfully and stepping motion bas been demonstrated. Fig. 3 shows a photograph of the micromotor.

These examples show what kind of studies can be done with such a tool. It can be easily employed in a design procedure and can be linked to other CAD tools, like mask design. Since mcshing can be done automatically, all the simulation procedure can be pil oted by a superviser in which parametric programming can be implemented.

Simulation of the dynamic bchaviour

After a micromotor design bas been chosen, its dynamic operation must be analyscd .

Electromechanical mode/

The dynamic bchaviour of the variable-capacitance micromotors can be modellcd by the diffcrential matrix equations [START_REF] Sarraute | Modclisation and simulation of the dynamic working of variables capacitances micromotors[END_REF]: a

! [Q(r)J = [Rr 1[vcr)J-[Rr 1[cc acr))r 1 [Q(r)J ! û(t) ={T,(
T e (t) = 2 [U (t) ] t ae [ C( 0(t)) ][ U (t) ] ( 2
)
where [ U (t)] is the potential vector on each electrode of the machine. B is the viscous friction coefficient.

The dry friction torque depends on two coefficients. The constant term C 1 takes into account the rotor weight. The term C 2 U s 2 takes into account the axial and radial efforts, which are functions of the square of the potential applied on the stator electrodes. J is the inertial coefficient.

Computation of the electrical parameters

The matrix of resistances [R] is constant and can be easily guessed from the physical and geometrical char-

Calculation of the mechanical parameters

The parameters J, B, C 1 and C 2 are calculated an alytically [START_REF] Sarraute | Etude et modélisation de microactionncurs intégrés sur silicium[END_REF] or determined experimentally [START_REF] Bart | Elcctric micromotor dynamics[END_REF]. For the micromotor studied these parameters are equal to

J =2.8 X 10-20 N m rad-1 s-2 C 1 = 1.95 X 10-is N m B = 1.3 X 10-16 N m rad-1 s C 2 =2.96x10-11 Nm v-2 3.4. Simulation procedure (3)
For a given voltage [V(t)], the status variables of the system are the charge quantities [Q(t)], the angular speed D(t) and the angular position 0(t). The simulation procedure consists of determining first ail of the electromechanical model of the machine. Then, the resolution of the system (1) with a four-order Runge-Kutta method provides the dynamic response of the motor corresponding to the given voltage [V(t)].

Erample of application

We have simulated a start-up corresponding to a constant acceleration of the machine until a permanent rotational speed of 200 000 rpm is reached (Fig. 5). The acceleration is obtained by applying a linear vari ation of the electrical frequency with respect to time. When the frequency increases, the speed oscillations decrease, and the operation is just the same as that of a synchronous machine. The maximal rotational speed, limited by the drag torques, was calculated to be about 220 000 rpm for the studied structure [START_REF] Sarraute | Etude et modélisation de microactionncurs intégrés sur silicium[END_REF]. Many other types of operation, such as step positioning or quasi-dynamic operation can be studied, with different types of waveshapes of the supply voltages [START_REF] Sarraute | Modclisation and simulation of the dynamic working of variables capacitances micromotors[END_REF].

Conclusions

Two simulation proccdurcs for elcctromechanical de sign have been briefly dcscribed. These two procedures are bascd on a finite-element code. Finite-element analysis is a very powerful technique and is growing more and more flexible owing to the progress in data processing techniques. It can be implemented easily in a CAD integration for the design of micromotors. The examples treated show that this kind of tool allows us to design micromotors, to dcfinc the elcctronic supply strategies or simply to evaluatc bcttcr the fields of application of electric micromotors.

Fig. 1 .

 1 Fig. 1. Scalar equipotential lines of a 3/1 electric micromotor.

Fig. 2 .

 2 Fig. 2. Electric driving torque vs. rotor position when two stator phases are supplied.

Fig. 3 .

 3 Fig. 3. Side view of the fnbricatcd micromotor.

  t)-Bû(t)-(C1 +CP])sign(û(t})}governs the electrical beh.aviour of the motor. The currents, which are equal to the de rivative versus time of the charges on the electrodes [Q(t)], are related to the external supply voltages [V(t)] by the diagonal matrix of resistance [R] and the matrix of influence and capacitance coefficients [C(0(t))]. The two last equations describe the motion of the rotor. ü(t) is the angular speed of the rotor and 0(t) the angular position of the rotor. The rotor is submitted to the electrical torque T e (t), the viscous and diy friction torques. The electrical torque T e (t) is calculated by the angular derivation of the electrical co-energy of the system:

1

 1

3 Fig. 4 .

 34 Fig. 4. Coefficient of capacitance of one phase of the :;tator.

Fig. 5 .

 5 Fig. 5. A start-up by increasing the electrical power frequency linearly up to 20 kHz: (a) voltage supply; (b) angular position; (c) rotational speed; ( d) electric and drag torques.

  acteristics of the electrodes. The matrix [C(0)] depends on the angular position of the rotor. Its components are functions of the angular position of the rotor and are computed by means of the static model presented in Section 2. For example, Fig.4shows the coefficient of capacitance of one phase of the stator versus the angular position of the rotor.


J L Autran

D Munteanu

Single Event Effects: the effects of Single particles on electronics Space, aerospace and ground

Introduction

The integrated circuit (IC) sensitivity to radiation coming from the natural space or present in the terrestrial environment has been found to seriously evolve [START_REF] Dodd | Basic mechanisms and modeling of single-event upset in digital microelectronics[END_REF][START_REF] Baumann | Radiation-induced soft errors in advanced semiconductor technologies[END_REF][START_REF] Autran | Soft Errors: From Particles to Circuits[END_REF] as MOSFET dimensions have reduced. Nowadays, for ultra-scaled devices, natural radiation is inducing one of the highest failure rates of all reliability concerns for devices and circuits in the area of nano-electronics [START_REF] Baumann | Radiation-induced soft errors in advanced semiconductor technologies[END_REF]. In particular, ultra-scaled memory integrated circuits have been found to be more sensitive to single-event-upset (SEU) and digital devices more affected by digital single-event transient (DSETs). This sensitivity to Single Event Effects (SEE) is a direct consequence of the reduction of device dimensions and spacing within circuit blocks combined with the reduction of supply voltage and node capacitance, resulting in a decrease of both the critical charge (i.e. the minimum amount of charge required to induce a bit flip) and the sensitive area (i.e. the minimum collection area inside which a given particle can deposit enough charge to induce a bit flip) [START_REF] Baumann | Radiation-induced soft errors in advanced semiconductor technologies[END_REF], [START_REF] Mitra | Soft errors: Technology trends, system effects and protection techniques[END_REF].

This paper examines the issue of soft errors induced by natural radiation at ground level in current and future CMOS digital circuits. Four main topics will be addressed in the following:

• in a first part we briefly describe the natural radiation environment at ground and atmospheric levels; • the physics and the underlying mechanisms of soft errors at silicon level are summarized a second part. We briefly depict the main mechanisms of interaction between atmospheric radiation and circuit materials and the electrical response of transistors, cells and complete circuits.

• the third part explains soft error characterization using accelerated and real-time tests, as well as modelling and numerical simulation issues. • the fourth part presents and discusses the radiation response of advanced technologies, including decananometer bulk, FD-SOI and FinFET families.

Natural radiation environment at ground and atmospheric levels

Soft errors are the result of the interaction of highly energetic particles, such as protons, neutrons, alpha particles, or heavy ions, with the sensitive region(s) of a microelectronic device or circuit. A single event may perturb the device/circuit operation (e.g., reverse or flip the data state of a memory cell, latch, flip-flop, etc.) or definitively damage the circuit (e.g. gate oxide rupture, destructive latch-up events). The problem has been well known for space applications over many years (more than forty years) and production mechanisms of soft errors in semiconductor devices by energetic protons, electrons and heavy ions well apprehended, characterized and modelled [START_REF]Radiation Effects and Soft Errors in Integrated Circuits and Electronic Devices[END_REF]. In a similar way for avionic applications, the interaction of atmospheric high-energy neutrons and protons with electronics has been identified as the major source of soft errors [START_REF] Normand | Single event upset at ground level[END_REF]. For the most recent deca-nanometers technologies, the impact of other atmospheric particles produced in nuclear cascade showers on circuits has been clearly demonstrated, in particular low-energy protons [START_REF] Cannon | Heavy ion, high-energy, and low-energy proton SEE sensitivity of 90-nm RHBD SRAMs[END_REF] and more recently low-energy muons [START_REF] Sierawski | Muon-induced single event upsets in deep-submicron technology[END_REF]).

With respect to such high-altitude atmospheric environments, the situation at ground level is slightly different: atmospheric particle fluxes are divided by more than two order of magnitudes (÷300 for neutrons, ÷500 for protons) at sea level with respect to their values at avionics altitude. Such tenuous atmospheric radiation cannot longer screen telluric radiation (alpha particles generated from ultra-traces of radioactive contaminants in CMOS process or packaging materials) that can impact the soft error rate (SER) of circuits at ground level [START_REF] Ziegler | SER -History, Trends and Challenges[END_REF][START_REF] Autran | Soft-errors induced by terrestrial neutrons and natural alphaparticle emitters in advanced memory circuits at ground level[END_REF]. As a consequence of these multiple sources of radiation, the accurate modelling and simulation of the SER of circuits at ground level is rather a complex task because one can clearly separate the contribution to SER of atmospheric particles (the external constraint) from the one due to natural alpha-particle emitters present as contaminants in circuit materials (the internal constraint).

Physics and the underlying mechanisms of soft errors

The physical underlying mechanisms related to the production of soft errors in microelectronic devices schematically consist of three successive steps (Figure 1) [START_REF] Glorieux | Random-walk drift-diffusion charge-collection model for reverse-biased junctions embedded in circuits[END_REF]: (1) the charge deposition by the energetic particle within the sensitive region, (2) the transport of the released charge into the device and ( 3)-( 4) the charge collection in the active region of the device. In the following, we succinctly describe these different mechanisms at the origin of SEUs or SETs in digital circuits.

Charge deposition (or generation): When an energetic charged particle strikes the device, an electrical charge along the particle track can be deposited by one of the following mechanisms: direct ionization by the interaction with the material or indirect ionization, by secondary particles issued from nuclear reactions with the atoms of the struck material. Direct ionization by heavy ions (Z ≥ 2) of the space environment is particularly important. These interact with the target material mainly by inelastic interactions and transmit a large amount of energy to the electrons of the struck atoms. These electrons produce a cascade of secondary electrons, which thermalize and create electron-hole pairs along the particle path. In a semiconductor or insulator, a large amount of the deposited energy is thus converted into electron-hole pairs, the remaining energy being converted into heat and a very small quantity into atomic displacements. It was shown experimentally that the energy necessary for the creation of an electron-hole pair depends on the material bandgap. In a microelectronics silicon substrate (bulk material), one electron-hole pair is produced for every 3.6 eV of energy lost by the ion.

Other particles, such as the neutrons of the terrestrial environment, do not directly ionize the matter on their passage. However, these particles should not be neglected, because they can produce SEE due to their probability of nuclear reaction with the atoms of materials that compose the microelectronic devices. This mechanism is called indirect ionization. The charged products resulting from a nuclear reaction can deposit energy along their tracks, in the same manner as that of direct ionization. Since the creation of the column of electron-hole pairs of these secondary particles is similar to that of ions, the same general models and concepts can be used.

Charge transport: When a charge column is created in the semiconductor by an ionizing particle, the released carriers are quickly transported and collected by elementary structures (e.g. p-n junctions). The transport of charge relies on two main mechanisms: the charge drift in regions with an electric field and the charge diffusion in neutral zones. The deposited charges can also recombine with other mobile carriers existing in the lattice, especially in the early stage just after electron-hole pair generation.

Charge collection: The charges transported in the device induce a parasitic current transient, which can induce disturbances in the device and associated circuits. The devices most sensitive to ionizing particle strikes are generally devices containing reverselybiased p-n junctions, because the strong electric field existing in the depletion region of the p-n junction allows a very efficient collection of the deposited charge. The effects of ionizing radiation are different according to the intensity of the current transient, as well as the number of circuit nodes impacted. If the current is sufficiently important, it can induce permanent damage on gate insulators (single event gate rupture, SEGR) or the latch-up (single event latchup, SEL) of the device. In usual low-power circuits, the transient current may generally induce only an eventual change of the logical state (cell upset).

Soft error characterization and modelling issues

Soft error characterization: accelerated and realtime tests

To predict the impact of natural radiation on the behavior of electronics and to (statistically) estimate (i.e. measure) its radiation-induced soft error rate (SER), three main experimental approaches can be envisaged [START_REF] Ziegler | SER -History, Trends and Challenges[END_REF], [START_REF] Jedec | Measurement and reporting of alpha particles and terrestrial cosmic ray-induced soft errors in semiconductor devices[END_REF], excluding modelling and simulation methods that can be used, under certain conditions (i.e. when correctly calibrated), as predictive tools.

The first one, called "field testing", consists in collecting errors from a large number of finished products already on the market. The SER value is evaluated a posteriori from the errors experienced by the consumers themselves; it takes generally several years after the introduction of the product on the market. This method is not adapted to upstream reliability studies performed during the cycle of product development and will not be considered in the following.

The second method, called "accelerated" soft error rate (ASER), consists in using intense particle beams or sources chosen for their to mimic the atmospheric (neutron) spectrum or to generate alpha particles within the same energy range than the alphas emitted by radioactive contaminants [START_REF] Ziegler | SER -History, Trends and Challenges[END_REF], [START_REF] Jedec | Measurement and reporting of alpha particles and terrestrial cosmic ray-induced soft errors in semiconductor devices[END_REF]. This accelerated SER (ASER) method is fast (data can be obtained in a few hours or days instead of months or years for the other methods), a priori easy to implement and only requires a few functional chips to estimate the SER. This allows the manufacturer to perform such radiation tests relatively early in the production cycle. Another major and growing advantage is its capability to quantify from a very large statistics (cumulated number of events) the importance of multiple cell/multiple bit upsets in the radiation response of ICs fabricated in technological nodes typically below 65 nm. But data can be potentially tainted by experimental artifacts (more or less well controlled according to the facility, the experimental setup or other various experimental conditions). As a direct consequence, ASER results must be extrapolated to use conditions and several different radiation sources must be used to ensure that the estimation accounts for soft errors induced by both alpha particle and cosmic-ray-neutron events.

The third method consists in exposing a given device (or a large number of identical devices) to terrestrial radiation over a sufficiently long period (weeks or months) in order to achieve adequate statistics on the number of accumulated errors and then on the SER value. This method is called "real-time" soft error rate (RTSER) test [START_REF] Autran | Altitude and underground real-time SER characterization of CMOS 65nm SRAM[END_REF][START_REF] Autran | Real-time soft-error testing of 40nm SRAMs[END_REF][START_REF] Autran | Real-time soft-error rate measurements: A review[END_REF][START_REF] Autran | Altitude and under-ground real-time SER testing of SRAMs manufactured in CMOS bulk 130, 65 and 40 nm[END_REF] or unaccelerated testing. In this method, as in accelerated testing, the intensity of the natural radiation can be increased by deploying the test in altitude (at least for neutrons, Figure 2). However, the acceleration factor AF (i.e. the ratio of the neutron integrated flux at the test location divided by its reference value at New-York City, NYC [START_REF] Jedec | Measurement and reporting of alpha particles and terrestrial cosmic ray-induced soft errors in semiconductor devices[END_REF]) has nothing to do with those reached in accelerated tests. Considering an equivalence of the radiation background composition in altitude and at sea level [START_REF] Jedec | Measurement and reporting of alpha particles and terrestrial cosmic ray-induced soft errors in semiconductor devices[END_REF], typical AF values between 5 and 20 as a function of the test location on Earth, can be expected. Devices have thus to be tested for a long enough period of time (months or years) until enough soft errors have been accumulated to give a reasonably confident estimate of the SER. The main advantage of RTSER tests is that they provide a direct measurement of the "true" SER that does not require intense radiation sources and extrapolations to use conditions. The major drawbacks of this method concern the cost of the system (which has to be capable of monitoring a very large number of devices at the same time) and the long duration of the experiment.

Soft error modelling

Modelling and simulating the effects of ionizing radiation has long been used for better understanding radiation effects on the operation of devices and circuits. In the last two decades, due to substantial progress in simulation codes and computer performances that reduce computation times, simulation has acquired significantly increased interest [START_REF] Dodd | Physics-based simulation of single-event effects[END_REF][START_REF] Munteanu | Modeling and simulation of single-event effects in digital devices and ICs[END_REF]. Due to its predictive capability, simulation offers the possibility to reduce radiation experiments and to test hypothetical devices or conditions, which are not feasible (or not easily measurable) by experiments. The continuous reduction of the feature size in microelectronics requires increasingly complicated and time-consuming manufacturing processes. Therefore, a systematic experimental investigation of the radiation effects of new ultrascaled devices or emerging devices with alternative architecture (such as multiple-gate or silicon nanowire transistors) is difficult and expensive. Since computers are today considerably cheaper resources, simulation is becoming an indispensable tool for the device engineer, not only for the device optimization, but also for specific studies such as the device sensitivity when subjected to ionizing radiation. Last but not least, the understanding of the soft error mechanisms in ultrascaled devices and the prediction of their occurrence under a given radiation environment are of fundamental importance for certain applications requiring a very high level of reliability and dependability [START_REF] Ziegler | SER -History, Trends and Challenges[END_REF].

Radiation response of advanced technologies

While CMOS technologies continue to shrink in a "More Moore" perspective, new risks are arising with scaling for single event effects (SEE). Indeed, the SEE susceptibility of advanced technologies is expected to evolve under the influence of several factors since extrinsic radiation does not scale down. The most important are [START_REF] Roche | Technology downscaling worsening radiation effects in bulk: SOI to the rescue[END_REF][START_REF] Massengill | Technology scaling and soft error reliability[END_REF]: 1) the reduction of the critical charge, 2) the reduction of the per-bit cross-sections presented to ionizing particles, 3) the reduction of the energy-deposition volumes traversed by the particle at front-end level, 4) the increase of the particle region of influence at layout level and 5) the amplification of parasitic effects as a function of device architecture considered.

Figure 1 .

 1 Figure 1. Mechanisms of Soft Errors: particle Monte Carlo Simulation (RWDD model -IM2NP).

Figure 2 .

 2 Figure 2. IM2NP/REER real-time test platforms.