William M Jackson

Festschrift " Sydney Leach

Nykola C Jones

Søren V Hoffmann

Sun Un

VUV Absorption Spectra of Gas-Phase Quinoline in the 3 .5 -1 0 .7 eV Photon Energy Range Published as part of The Journal of Physical Chemistry virtual special issue "

The absorption spectrum of quinoline was measured in the gas phase between 3.5 and 10.7 eV using a synchrotron photon source. A large number of sharp and broad spectral features were observed, some of which have plasmon-type collective π-electron modes contributing to their intensities. Eight valence electronic transitions were assigned, considerably extending the number of π-π* transitions previously observed mainly in solution. The principal factor in solution red-shifts is found to be the Lorentz-Lorenz polarizability parameter. Rydberg bands, observed for the first time, are analyzed into eight different series, converging to the D 0 ground and two excited electronic states, namely, D 3 and D 4 , of the quinoline cation. The R1 series limit is 8.628 eV for the first ionization energy of quinoline, a value more precise than previously published. This value, combined with cation electronic transition data, provides precise energies, respectively, 10.623 and 11.355 eV, for the D 3 and D 4 states. The valence transition assignments are based on density functional theory (DFT) calculations as well as on earlier Pariser-Parr-Pople (P-P-P) selfconsistent field linear combination of atomic orbitals molecular orbital results. The relative quality of the P-P-P and DFT data is discussed. Both are far from spectroscopic accuracy concerning electronic excited states but were nevertheless useful for our assignments. Our time-dependent DFT calculations of quinoline are excellent for its ground-state properties such as geometry, rotational constants, dipole moment, and vibrational frequencies, which agree well with experimental observations. Vibrational components of the valence and Rydberg transitions mainly involve C-H bend and CC and CN stretch modes. Astrophysical applications of the vacuum UV absorption of quinoline are briefly discussed.

I. INTRODUCTION

The aza-arene quinoline contains a benzene ring fused to a pyridine molecule. It is analogous to naphthalene and is indeed one of the smallest examples of polycyclic aromatic nitrogen heterocycles (PANHs), the nitrogen analogues of the polycyclic aromatic hydrocarbons habitually denoted as PAHs. PANHs have been observed or suspected to exist in planetary atmospheres, [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] the interstellar medium, [START_REF] Mattioda | Infrared Spectroscopy of Matrix-Isolated Polycyclic Aromatic Compounds and Their Ions. 6. Polycyclic Aromatic Nitrogen Heterocycles[END_REF][START_REF] Elsila | UV Photolysis of Quinoline in Interstellar Ice Analogs[END_REF][START_REF] Tielens | The Molecular Universe[END_REF] and other astrophysical sites. [START_REF] Tielens | The Molecular Universe[END_REF][START_REF] Stoks | Basic Nitrogen-Heterocyclic Compounds in the Murchison Meteorite[END_REF][START_REF] Sephton | Organic Compounds in Carbonaceous Meteorites[END_REF] The spectroscopic properties of quinoline, in particular in the gas phase, is thus of potential interest in astrophysical studies and observations, as well as for cosmochemical theoretical simulations.

Quinolines have also quite extensive chemical, biological, and practical uses, [START_REF] Prajapati | Recent Advances in the Synthesis of Quinolines: A Review[END_REF] as catalysts and corrosion inhibitors in metallurgical processes, in the manufacture of dyes, and as a solvent for resins and terpenes, although their main use is as a feedstock in the production of other chemicals. [START_REF] Greenhill | The Chemistry of Heterocyclic Compounds, Quinolines[END_REF] Quinoline is also used as an antimalarial medicine. [START_REF] Marella | A Versatile Heterocyclic[END_REF] Although there have been many studies of absorption spectra of quinoline in the near-UV region, mainly in solution or in matrices, there have been few studies of its gas-phase absorption spectra. Extensive work has been done on its fluorescence and phosphorescence spectra. [START_REF] Innes | Electronic States of Azabenzenes and Azanaphthalenes: A Revised and Extended Critical Review[END_REF] Measurements of the absorption spectra of quinoline in the period of 1922-1943 are cited by Ewing and Steck [START_REF] Ewing | Absorption Spectra of Heterocyclic Compounds: Quinolinols and Isoquinolinols[END_REF] in their pioneer modern study of the effects of solvent pH on these spectra. The earliest gas-phase absorption spectrum, which dates from 1910, [START_REF] Purvis | The Absorption Spectra of Nicatine, Coniine and Quinoline as Vapours, Liquids and Solution[END_REF] is a photographic plate spectrum of quinoline absorption in which, using a cadmium spark as a quasi-continuum source, a broad band was observed in the near-ultraviolet (band wavelengths not specified). The more recent gas-phase absorption measurements of quinoline [START_REF] Innes | Electronic States of Azabenzenes and Azanaphthalenes: A Revised and Extended Critical Review[END_REF][START_REF] Amma | Infrared and Electronic Absorption Spectra of Quinoline[END_REF][START_REF] Okajima | Radiationless Transitions in Gaseous Nitrogen Heterocyclics: Energy Dependence of Internal Conversion in Quinoline and Isoquinoline[END_REF][START_REF] Hiraya | Identification of the Lowest Energy nπ* States in Gas-Phase Polycyclic Monoazines: Quinoline and Isoquinoline[END_REF] are restricted to the near-UV in the 3.8-4.5 eV region, while solution absorption spectra of quinoline have an upper photon energy limit of ∼5.4 eV. [START_REF] Innes | Electronic States of Azabenzenes and Azanaphthalenes: A Revised and Extended Critical Review[END_REF][START_REF] Favini | Electronic Spectra of Mono-, Di-and Tri-Azines of the Naphthalene Series[END_REF][START_REF] Muller | Absorptions-und Phosphoreszspektren der Mono-und der Diazanaphthaline (π-π-Phosphoreszenz nach n-π-Absorption bei den Diazanaphthalinen)[END_REF] An absorption spectrum of liquid quinoline up to 10.6 eV has also been measured. [START_REF] Macrae | Optical Properties of Some Aromatic Liquids in the Vacuum Ultraviolet[END_REF] The Aarhus synchrotron radiation source enabled us to extend absorption spectral measurements of gas-phase quinoline up to 10.7 eV, to identify eight valence transitions, to discover eight previously unknown Rydberg series of bands converging to ground and excited electronic states of the ion, and to measure the absorption cross sections over the 3.6-10.7 eV region, of crucial importance in cosmochemical process modeling.

II. EXPERIMENTAL SECTION

II.1 . Absorption Measurements. The absorption measurements were performed on the AU-UV beamline at the ASTRID2 synchrotron facility in Aarhus, Denmark. A detailed description of the AU-UV beamline, its resolution possibilities, and procedure for determining absorption cross sections is given by Palmer et al. [START_REF] Palmer | Interpretation of the Vacuum Ultraviolet Photoabsorption Spectrum of Iodobenzene by ab initio Computations[END_REF] The quinoline samples were introduced at room temperature into a gas cell with a path length (l) of 15.5 cm, whose entrance and exit MgF 2 windows are effectively transparent in the vacuum ultraviolet (VUV) down to ∼10.8 eV (115 nm). A toroidal dispersion grating provided VUV radiation at selective energies; wavelength scans were performed with step sizes ranging from 0.05 to 0.2 nm, chosen according to the level of structure in different regions of the spectrum. The intensity of the light transmitted through the gas (I t ) is measured by a UV-VUV sensitive photomultiplier (ET Enterprises 9406B). There is a small gap between the exit window of the gas cell and the recording photomultiplier. This gap is evacuated, thus preventing air contamination, to maintain transparency at photon energies above 5.5 eV. At lower energies, air is allowed into this gap to remove higher-order radiation, while the MgF 2 entrance window of the cell prevents higher-order radiation above 11 eV. Gas pressure is measured by a heated baratron capacitance manometer (Inficon CDG100D). The synchrotron beam current is measured during each wavelength scan, and the measured intensity is normalized to this current. A background scan is recorded with the cell evacuated (I o ).

Absorption cross sections were determined, with a general accuracy of ±5%, using the Beer-Lambert law: I t = I 0 exp(nσl). The quinoline sample, of highest purity commercially available (Sigma-Aldrich), was prepared for use with four freeze-pump-thaw cycles and used without further treatment.

II.2 . Computational Methods and Results. Quinoline is a heterocyclic planar molecule belonging to the C s symmetry group. We are interested in calculations of the valence transitions of quinoline to aid in spectral transition assignments, the π-π* transitions, in particular. There are many reported quantum mechanical computations of these quantities, mainly by Pariser-Parr-Pople (P-P-P) methods as discussed in Section III.1. We found these useful for spectral assignments but thought it worthwhile to perform timedependent density functional theory (TD-DFT) calculations for comparison. We note that the TD-DFT formalism derived from Kohn-Sham theory can also be considered as an empirically corrected variant of the random-phase approximation (RPA) in Hartree-Fock theory. [START_REF] Stratmann | An Efficient Implementation of Time-Dependent Density-Functional Theory for the Calculation of Excitation Energies of Large Molecules[END_REF][START_REF] Cai | Failure of Density-Functional Theory and Time-Dependent Density-Functional Theory for Large Extended π Systems[END_REF] Our quantum chemical calculations were performed using the Gaussian 09 program, revision C.01. [START_REF] Frisch | Gaussian 0 9[END_REF] Initial geometry optimization of quinoline was performed using the hybrid density functional B3LYP and 6-31+G(d,p) basis set. Normal mode analysis confirmed that the final optimized geometry was a true potential energy minimum. This structure was used to perform TD-DFT using the CMB3LYP hybrid densityfunctional [START_REF] Yanai | A New Hybrid Exchange-Correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP)[END_REF] and the 6-31+G(d,p) basis-set.

II.2 .1 . Structural Properties. There are no reported direct measurements of the geometry of quinoline, but our calculated structural parameters (Figure 1) are in satisfactory agreement with other calculated values. [START_REF] Bandyopadhyay | Force Field and Assignment of the Vibrational Spectra of Quinoline and Isoquinoline-An ab initio Study[END_REF][START_REF] Buÿukmurat | Infrared-Spectra and Normal-Coordinate Analysis of Quinoline and Quinoline Complexes[END_REF][START_REF] Kisiel | Rotational Spectra of Quinoline and Isoquinoline: Spectroscopic Constants and Electric Dipole Moments[END_REF][START_REF] Moomaw | Strained Heterocyclic Systems.10. Photoelectron Spectra and Theoretical Studies of Bonding in Strained Quinolines[END_REF] Experimental values of gasphase ground-state rotational constants are known from highresolution microwave and/or optical spectroscopy measurements. [START_REF] Kisiel | Rotational Spectra of Quinoline and Isoquinoline: Spectroscopic Constants and Electric Dipole Moments[END_REF][START_REF] Moomaw | Strained Heterocyclic Systems.10. Photoelectron Spectra and Theoretical Studies of Bonding in Strained Quinolines[END_REF][START_REF] Pirali | Rotation-Vibration Interactions in the Spectra of Polycyclic Aromatic Hydrocarbons: Quinoline as a Test-Case Species[END_REF][START_REF] Martin-Drumel | Lowest Energy Vibrational Modes of Some Natphthalene Derivatives: Azulene, Quinoline, Isoquinoline-Experiment and Theory[END_REF] Our calculated rotational constants are in quite good agreement with the experimental values for quinoline (Table 1). Another criterion of quality for the ground electronic state is the dipole moment. Our calculated values of the dipole moment are in very good agreement with quinoline values obtained from gas-phase polarization measurements, [START_REF] Buckingham | The Dipole Moments of Pyridine, Quinoline, and Isoquinoline as Vapours and as Solutes[END_REF] but are ∼12% larger than the Stark effect values (Table 1). Determining the dipole moment from polarization measurements in the gas phase requires measurements that extend over a temperature range of at least 100 K. This condition was fulfilled in the measurements of Buckingham et al. [START_REF] Buckingham | The Dipole Moments of Pyridine, Quinoline, and Isoquinoline as Vapours and as Solutes[END_REF] Uncertainties in Stark effect measurements of gas-phase dipole moments are discussed by Kisiel et al. [START_REF] Kisiel | Rotational Spectra of Quinoline and Isoquinoline: Spectroscopic Constants and Electric Dipole Moments[END_REF] A wide range of calculated values of the dipole moment of quinoline given by a varied set of quantum mechanical 2 and3, used for general interest as comparative tests for various calculation methods of vibrational frequencies. The experimental frequencies reported by Wait and McNerney are from their infrared and Raman study in liquid-and/or in gas-phase quinoline. Mode assignments were made on the basis of normal coordinate analysis using the Urey-Bradley force field including Kekulémodification with force constants transferred from naphthalene and s-triazine. High-resolution gas-phase far-infrared spectroscopy, performed by Martin-Drumel et al. [START_REF] Martin-Drumel | Lowest Energy Vibrational Modes of Some Natphthalene Derivatives: Azulene, Quinoline, Isoquinoline-Experiment and Theory[END_REF] with a Fourier transform instrument also provided frequencies for modes 28, 31, 40, 41, 43, and 45. Millimeter-wave spectroscopy was used by Pirali et al. [START_REF] Pirali | Rotation-Vibration Interactions in the Spectra of Polycyclic Aromatic Hydrocarbons: Quinoline as a Test-Case Species[END_REF] to obtain high-resolution gas-phase values for the frequencies of modes 44 and 45.

Table 2 also includes the results of a force-field and vibrational spectral study of quinoline whose geometry was optimized at the Hartree-Fock level of theory using a 6-31G** basis set, performed by Bandyopadhyay and Manogaran. [START_REF] Bandyopadhyay | Force Field and Assignment of the Vibrational Spectra of Quinoline and Isoquinoline-An ab initio Study[END_REF] The ab initio values of the vibrational frequencies, given in the table, require severe scaling (0.7-1.0 for a′ modes and Table 2 . Quinoline Vibrational Frequencies (cm -1 ): Harmonic Frequency Calculations cf. Observed Values vibrational mode [START_REF] Wait | Vibrational Spectra and Assignments for Quinoline and Isoquinoline[END_REF] observed [START_REF] Wait | Vibrational Spectra and Assignments for Quinoline and Isoquinoline[END_REF] DFT harmonic present study DFT harmonic [START_REF] Martin-Drumel | Lowest Energy Vibrational Modes of Some Natphthalene Derivatives: Azulene, Quinoline, Isoquinoline-Experiment and Theory[END_REF] Hartree-Fock 24 force field refinement 25 0.5-1.0 for a″ modes) to bring them in line with observed values. An evaluation of various ab initio, semiempirical, and DFT methods of calculation of molecular harmonic vibrational frequencies has been made to determine optimal frequency scaling factors. [START_REF] Hamprecht | Development and Assessment of New Exchange-Correlation Functionals[END_REF][START_REF] Scott | Harmonic Vibrational Frequencies: An Evaluation of Hartree-Fock, Møller-Plesset, Quadratic Configuration Interaction, Density Functional Theory, and Semiempirical Scale Factors[END_REF] The final right-hand column in Table 2 gives the results of a theoretical study by O ̈zel et al. [START_REF] Buÿukmurat | Infrared-Spectra and Normal-Coordinate Analysis of Quinoline and Quinoline Complexes[END_REF] using a force-field refinement method in which the force-field parameters of quinoline were determined by refinement of the corresponding parameters of benzene and pyrimidine molecules, taking into account the results of semiempirical and ab initio calculations. This gave frequency values in very reasonable agreement with observed values for many, but not all, vibrational modes. A comparison of the calculated frequencies in the various studies represented in Table 2 shows that the DFT harmonic calculations provide reasonable values that require far less scaling or refinement techniques to simulate observed values, consistent with the conclusions of the study of Scott and Radom. [START_REF] Scott | Harmonic Vibrational Frequencies: An Evaluation of Hartree-Fock, Møller-Plesset, Quadratic Configuration Interaction, Density Functional Theory, and Semiempirical Scale Factors[END_REF] It is well-known that harmonic vibrational frequencies derived from DFT calculations require scaling. The B3LYP/ 6-31+G(d,p) anharmonic frequencies calculated using the second-order vibrational perturbation theory implemented by Barone 35 in Gaussian 09 required essentially no scaling (Table 3). The root-mean-squared deviation of these anharmonic values from the observed was 23 cm -1 with a maximum absolute deviation of 85 cm -1 . They were in general closer in value than those obtained by Martin-Drumel et al. [START_REF] Martin-Drumel | Lowest Energy Vibrational Modes of Some Natphthalene Derivatives: Azulene, Quinoline, Isoquinoline-Experiment and Theory[END_REF] with the hybrid B97-1 functional and the 6-311G(d,p) basis set. This appeared to be largely due to the different implementations of the second-order vibrational perturbation theory in the two different versions of Gaussian used. When the B97-1/6-311G(d,p) anharmonic frequencies were recalculated using the method of Barone, 35 their correlation to the observed values was markedly improved and was only statistically slightly worse than those using B3LYP/6-31+G(d,p). Better results were obtained using B97-1/6-311+G(d,p) with a root-mean-squared deviation of 17 cm -1 and a maximum deviation of 82 cm -1 . Thus, as expected, the results of DFT anharmonic calculations come closer to experimental values and can generally be more useful in vibrational mode assignments. II.2 .3 . Electronic State Energies and Transition Oscillator Strengths. The energies and oscillator strengths of transitions to the first 33 singlet electronic excited states of quinoline up to 8.214 eV (13 A′ states, 19 A″ states) were calculated using the TD-DFT method [START_REF] Stratmann | An Efficient Implementation of Time-Dependent Density-Functional Theory for the Calculation of Excitation Energies of Large Molecules[END_REF] with the same hybrid density function and basis set. The eigenvalues are critically dependent on molecular orbital (MO) energy differences in TD-DFT calculations, so that the calculations may not provide reliable values for transition energies. This has proved to be the case as discussed later in the valence transition assignments of the absorption spectra of quinoline. However, these calculations enable us to differentiate between strong and weak electronic transitions, since DFT-calculated oscillator strengths are not very sensitive to the exactness of calculated transition energies, [START_REF] Wasserman | Accurate Rydberg Excitations from the Local Density Approximation[END_REF][START_REF] Burke | Time-Dependent Density Functional Theory: Past, Present, and Future[END_REF] thus facilitating certain aspects of the valence transition assignments. However, particular transition oscillator strengths can be distorted if there is interaction with plasmontype effects (see later). The calculated transition energies and oscillator strengths are listed in Table 4.

III. RESULTS AND DISCUSSION

III.1 . Quinoline VUV Absorption Spectrum. The complete absorption spectrum of gas-phase quinoline between 3.6 and 10.7 eV is given in Figure 2. It includes a 10× intensity magnification insert between 3.8 and 5.6 eV. The spectrum is very rich in features, many of which are small peaks lying on diffuse continua, and some are present as shoulders in the absorption signal. The 137 measured features can be seen in more detail in intensity zooms of various sections of the absorption spectrum. Typical examples are given in Figures 345678for the spectral regions of 3.5-5.0, 4.5-5.8, 5.5-6.2, 6.5-7.8, 7.5-8.7, and 8.5-10.7 eV, respectively. Measurement of band energies was based on clear peaks evidenced as maxima in the recorded absorption cross sections as well as gradients in the cross sections in cases of less well-resolved features. The precision of peak energy pointing was between ±0.0006 and ±0.004 eV, depending on the spectral range and the step size in the wavelength scan. The measured features are listed as band numbers, energies, and band assignments in Table 5. These assignments are based, in part, on the results of electronic energy and transition-strength calculations by various quantum-mechanical methods discussed below.

Innes et al. [START_REF] Innes | Electronic States of Azabenzenes and Azanaphthalenes: A Revised and Extended Critical Review[END_REF] have listed the triplet and singlet energy level energies and strengths of n-π* and π-π* transitions of quinoline as evaluated in 1988. Similar data, limited to π-π* transitions, were published earlier by Baba and Yamzaki [START_REF] Baba | Interpretation of Electronic Spectra by Configuration Analysis. Absorption Spectra of Azanaphthalenes[END_REF] in connection with their molecular orbital calculation study of quinoline absorption spectra, using the Pariser-Parr-Pople self-consistent field (SCF) linear combination of atomic orbitals (LCAO) molecular orbital (MO) method. They calculated nine π-π* transitions up to 7.11 eV, as did Nishimoto, [START_REF] Nishimoto | The Variable Core Approach in the SCF MO Calculation of Heteroatomic Systems[END_REF] whose SCF MO calculations used a fixed core approximation, while eight calculated transitions in this energy region are reported by Tinland, [START_REF] Tinland | SCF MO Calculations of Ultraviolet Electronic Spectra of Azanaphthalenes with the Variable Beta Approximation[END_REF] using the P-P-P SCF LCAO MO method, and by Ridley and Zerner 41 who used a 6). We note that configuration interactions were included in several studies. [START_REF] Baba | Interpretation of Electronic Spectra by Configuration Analysis. Absorption Spectra of Azanaphthalenes[END_REF][START_REF] Ridley | The Calculated Spectra of the Azanaphthalenes[END_REF][START_REF] Wagner | LCI Pariser-Parr-Pople Calculations of π-Electron Systems in Nitrogen-Heterocyclic Molecules. Correlation with Spectral Data[END_REF] More limited π-π* transition calculations were performed by Favini et al. [START_REF] Favini | Electronic Spectra of Mono-, Di-and Tri-Azines of the Naphthalene Series[END_REF] and by Mataga [START_REF] Mataga | A Theory of the Electronic Spectra of Nitrogen Heterocycles: Azanaphthalenes and Azaanthracenes[END_REF] to interpret solution spectra, as well as by Wagner et al. [START_REF] Wagner | LCI Pariser-Parr-Pople Calculations of π-Electron Systems in Nitrogen-Heterocyclic Molecules. Correlation with Spectral Data[END_REF] who reported three π-π* transitions up to 5.78 eV (Table 6), while Goodman and Harrell 44 made analogous calculations on n-π* transitions. The results of these works, and of our own DFT calculations (Table 6), have helped in assigning the various sharp and broad features of quinoline valence transitions in our gas-phase absorption spectrum, which is described below, divided into a number of energy sectors. We also observed Rydberg transition bands for the first time. There are no reported calculations of quinoline Rydberg states.

We base our π-π* transition analysis and discussion mainly on the calculations of Baba and Yamakazi, [START_REF] Baba | Interpretation of Electronic Spectra by Configuration Analysis. Absorption Spectra of Azanaphthalenes[END_REF] whose transition energies and oscillator strengths are in excellent agreement with those of Nishimoto [START_REF] Nishimoto | The Variable Core Approach in the SCF MO Calculation of Heteroatomic Systems[END_REF] and in satisfactory agreement with those of Tinland [START_REF] Tinland | SCF MO Calculations of Ultraviolet Electronic Spectra of Azanaphthalenes with the Variable Beta Approximation[END_REF] and of Ridley and Zerner. [START_REF] Ridley | The Calculated Spectra of the Azanaphthalenes[END_REF] Our DFTcalculated transition energies are consistently greater than those of the older, mainly P-P-P, calculations and were generally found to be less useful for spectral assignment. We note, however, that our DFT calculations indicate that, for quinoline, of the 20 n-π* transitions (Table 4), only one, 5A″-1A′ calculated energy 6.822 eV, f = 0.0278, would have an oscillator strength of sufficient value to be observable in our spectra. These energies correspond to regions of overlying well-assigned Rydberg and valence bands.

III.1 .1 . Valence Transitions: 3 .6 -5 .4 eV. Transitions to the 2 1 A′ and 3 1 A′ Electronic States. This part of the spectrum has previously been studied in solution and in the vapor phase.

There are structured features in the 3.8-4.6 eV region (Figures 2 and3). The energy of the initial principal peak, measured at 3.991 eV (32 190 cm -1 ), is assigned to the 2 1 A′ ← 1 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A O 0 0 origin (see below). It agrees well with the values of other vapor-phase studies: 32 196 cm -1 that we determined from Figure 6 of a published vapor-phase absorption spectrum of quinoline by Okajima and Lim 14 and 32 192 cm -1 from a resonance-enhanced two-photon ionization spectrum. [START_REF] Hiraya | Identification of the Lowest Energy nπ* States in Gas-Phase Polycyclic Monoazines: Quinoline and Isoquinoline[END_REF] In condensed phases the first peak is shifted to lower energies by amounts, generally less than ∼350 cm -1 , dependent on the solvent. These redshifts for quinoline arise, in part, because of possibilities of forming hydrogen bonds with solvents containing -OH groups. Another factor in determining the position of the 2 1 A′ ← 1 1 A origin band concerns displacements due to interaction between the lowest excited n-π* and π-π* levels (see below) that will be affected differently in polar and nonpolar solvents. This is linked to the major factor in solvent shifts that is due to the electrostatic work required to produce the solute transition dipole, and this is a function of the particular dielectric medium enveloping the solvent. The observed redshifts for quinoline are consistent with the evolution of the Lorentz-Lorenz polarizability parameter of the solvent P = (n 2 -1)/(n 2 + 2), [START_REF] Reichardt | Solvents and Solvent Effects in Organic Chemistry[END_REF][START_REF] Bensasson | C 60 in Model Biological Systems. A Visible-UV Absorption Study of Solvent-Dependent Parameters and Solute Aggregation[END_REF] n being the solvent index of refraction in the 313 nm region. [START_REF] Sassara | Absorption Wavelengths and Bandwidths for Interstellar Searches of C 60 in the 2400-4100 Å Region[END_REF] The observations are as follows. In an argon matrix at 11 K (P = 0.181) the redshift is 88 cm -1 , 48 ∼215 cm -1 in a methanol matrix at 10 K 48 (P = 0.2152), ∼190 cm -1 in an ethanol matrix at 93 K 49 (P = 0.2358), ∼210 cm -1 in a room-temperature ethanol solution [START_REF] Muller | Absorptions-und Phosphoreszspektren der Mono-und der Diazanaphthaline (π-π-Phosphoreszenz nach n-π-Absorption bei den Diazanaphthalinen)[END_REF] (P = 0.2358), ∼240 cm -1 in a roomtemperature cyclohexane solution [START_REF] Favini | Electronic Spectra of Mono-, Di-and Tri-Azines of the Naphthalene Series[END_REF] (P = 0.2723), and ∼260 cm -1 in a 3-methyl pentane matrix at 77 K 50 (P = 0.284).

The structured features in the 3.6-5.4 eV energy frame are assigned to two π-π* transitions, namely, 2 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′, whose origin band at 3.991 eV has a calculated energy 4.09 eV [START_REF] Baba | Interpretation of Electronic Spectra by Configuration Analysis. Absorption Spectra of Azanaphthalenes[END_REF] (f = 0.060), and the 3 1 A′ ← 1 1 A′ transition, whose origin we assign to the band at 4.441 eV, in reasonable agreement with the value ∼4.22 eV listed by Innes et al. [START_REF] Innes | Electronic States of Azabenzenes and Azanaphthalenes: A Revised and Extended Critical Review[END_REF] (see also below). We remark that, from our DFT calculations, the 1 1 A″ ← 1 1 A′ n-π* transition is also expected in this energy region, below, but close to, the π-π* 2 1 A′ ← 1 1 A′ origin (Table 4). Favini et al. [START_REF] Favini | Electronic Spectra of Mono-, Di-and Tri-Azines of the Naphthalene Series[END_REF] assigned a cyclohexane solution spectrum band at 3.96 eV to n-π* and consider a band maximum at 4.59 eV, as do Amma et al. at 4.52 eV in the gas-phase spectrum, [START_REF] Amma | Infrared and Electronic Absorption Spectra of Quinoline[END_REF] to be due to a π-π* transition, which both groups consider (erroneously) to be the first π-π* transition 2 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′. According to the gas-phase observations of Hiraya et al., [START_REF] Hiraya | Identification of the Lowest Energy nπ* States in Gas-Phase Polycyclic Monoazines: Quinoline and Isoquinoline[END_REF] the very weak 1 1 A″ ← 1 1 A′ n-π* transition occurs close to the π-π* spectral region, with a transition origin band at 30 388 cm -1 (3.768 eV), ∼1850 cm -1 below the π-π* transition. This n-π transition is too weak to be observed in our absorption study. Indeed our DFT calculations predict the 1 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A″ ← 1 1 A′ n-π* transition oscillator strength to be ∼10 times weaker than that of the 2 1 A′ ← 1 1 A′ π-π* transition (Table 4).

In the high-resolution gas-phase spectrum of Hiraya et al. [START_REF] Hiraya | Identification of the Lowest Energy nπ* States in Gas-Phase Polycyclic Monoazines: Quinoline and Isoquinoline[END_REF] the π-π* origin band is complex, indicative of near-resonance vibronic coupling between the n-π*1 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A″ and π-π* 2 1 A′levels. Our 3.991 eV (32 190 cm -1 ) band peak has an absorption cross-section of 8.91 Mb, and it has two companion features, one at -56 cm -1 (8.42 Mb) and the other at +42 cm -1 (8.20 Mb) (Table 5). These energy values are in excellent agreement with the corresponding features at -59 and +39 cm -1 from their origin band peak at 32 192 cm -1 that we measured from Figure 2 of the resonance-enhanced twophoton ionization spectrum of Hiraya et al. [START_REF] Hiraya | Identification of the Lowest Energy nπ* States in Gas-Phase Polycyclic Monoazines: Quinoline and Isoquinoline[END_REF] The envelope of these three features in our spectrum (Figure 3) has a full width at half-maximum (fwhm) value of ∼30 meV, which is consistent with the profile of the complex origin band in the resonance-enhanced two-photon ionization spectrum and with the fwhm of the corresponding band in the Ar matrix spectrum. [START_REF] Creṕin | A Site-Selective Spectroscopy of Naphthalene and Quinoline in TEOS/ MTEOS Xerogels[END_REF] The other spectral features in the 3.8-4.4 eV region are mainly vibrational components of the lowest singlet-singlet π-π* transition. They have corresponding features in the condensed-phase absorption spectra, [START_REF] Purvis | The Absorption Spectra of Nicatine, Coniine and Quinoline as Vapours, Liquids and Solution[END_REF][START_REF] Amma | Infrared and Electronic Absorption Spectra of Quinoline[END_REF][START_REF] Creṕin | A Site-Selective Spectroscopy of Naphthalene and Quinoline in TEOS/ MTEOS Xerogels[END_REF][START_REF] Anton | Luminescence and Hydrogen Bonding in Quinoline and Isoquinoline[END_REF] while the published vapor-phase spectra concentrate only on the π-π* R4 δ = 0.645 origin band. An exception is an early photographic plate spectrum reported by Amma et al. [START_REF] Amma | Infrared and Electronic Absorption Spectra of Quinoline[END_REF] in which the π-π* transition features are observed at higher resolution and, as mentioned above, erroneously assigned to the n-π* transition.

We assign band number 5 at 4.080 eV to the vibronic transition 2 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′ x 1 0 , where the x vibrational mode of quinoline has a frequency of the order ν(x) ≈ 710 cm -1 . This is probably a C-H bend mode, whose ground-state frequency of 741 cm -1 is characteristic of the presence of four neighboring hydrogen atoms in quinoline. [START_REF] Coppens | Proprieteś Physico-chimiques de Composeś aCaractere Aromatique[END_REF] Amma et al. [START_REF] Amma | Infrared and Electronic Absorption Spectra of Quinoline[END_REF] report the analogous x 1 0 band in their vapor-phase spectrum at Δν = 707 cm -1 from their reputed origin band, whereas in the absorption spectrum of quinoline in an Ar matrix at 11 K of Creṕin et al., [START_REF] Creṕin | A Site-Selective Spectroscopy of Naphthalene and Quinoline in TEOS/ MTEOS Xerogels[END_REF] we determine from their Figure 3 a value of Δν ≈ 725 cm -1 . The corresponding value in a 3MP solvent at 77 K is Δν ≈ 690 cm -1 that we obtained from Figure 2 of the study by Anton and Moomaw. [START_REF] Anton | Luminescence and Hydrogen Bonding in Quinoline and Isoquinoline[END_REF] A number of other vibronic features of the 2 1 A′ ← 1 1 A′ transition were assigned to band nos. 5-12. These involve excitation of two other vibrational modes, namely, ν(y) ≈ 1050 cm -1 and ν(z) ≈ 1400 cm -1 . The ν(z) frequency is in the region characteristic of CC and CN stretching vibrations in the quinoline ground state. [START_REF] Bellamy | The Infrared Spectra of Complex Molecules[END_REF] Band no. 7 occurs at 44 cm -1 beyond the 2 1 A′ ← 1 1 A′ y 1 0 vibronic transition (Band no. 6) and so may be related to the +42 cm -1 component (Band no.

3) of the complex origin region.

We return now to the question of the energy of the second π-π* valence transition 3 1 A′ ← 1 1 A′, whose origin we assign to band no. 13 at 4.441 eV. The MO calculations of Baba and Yamazaki place 3 1 A′ ← 1 1 A′ transition at 4.32 eV, f = 0.123, [START_REF] Baba | Interpretation of Electronic Spectra by Configuration Analysis. Absorption Spectra of Azanaphthalenes[END_REF] while Nishimoto 39 calculates 4.527 eV, f = 0.163 (Table 6). Wagner et al. [START_REF] Wagner | LCI Pariser-Parr-Pople Calculations of π-Electron Systems in Nitrogen-Heterocyclic Molecules. Correlation with Spectral Data[END_REF] calculate this transition at 4.86 eV (f = 0.19) and consider it to correspond to the 1 L a (short axis polarized) transition in the nomenclature of Platt, based on his free electron model. [START_REF] Platt | Classification of Spectra of Cata-Condensed Hydrocarbons[END_REF] The 1 L a assignment was also made by Zimmerman and Joop [START_REF] Zimmerman | Polarisation der Elektronenbanden von Aromaten. 3. Mitteillung: Chinolin, Isochinolin, Indol[END_REF] on the basis of fluorescence polarization measurements. These authors state that, from their spectra of quinoline in ethanol solution, it is not possible to determine the precise energy of the 1 L a state origin, because it lies within the extensive 1 L b band region (Platt notation), that is, the 2 1 A′ ← 1 1 A′ transition region in our nomenclature. However, they do note that there is a marked minimum in the polarization spectrum at ∼4.35 eV, where one might expect to find the origin region of the 1 L a transition, in reasonable agreement with our assignment. We note also that, in magnetic circular dichroism (MCD) studies of quinoline in n-heptane solution by Kaito and Hitano [START_REF] Kaito | Experimental and Theoretical Studies on the Magnetic Circular Dichroism of Azanaphthalenes. Use of the CNDO/S-CI Approximation[END_REF] and by Vasǎḱ et al. [START_REF] Vasǎḱ | Magnetic Circular Dichroism of Cyclic π-Electron Systems.7. Aza Analogues of Naphthalene[END_REF] in cyclohexane solution, the 3 1 A′ ← 1 1 A′ origin is considered to be at ∼36 000 cm -1 (4.46 eV), where there is a minimum in the MCD curve.

The experimental and theoretical results discussed above are consistent with our assignment of the O 0 0 origin of the 3 1 A′ ← 1 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ transition to Band no. 13 at 4.441 eV. This occurs at the initial rising part of a broad continuous background 4.3-5.2 eV, discussed below. Band nos. 14 and 15 are assigned to vibronic components of the 3 1 A′ ← 1 1 A′ valence transition, involving ν(x) ≈ 700 cm -1 and ν(z) ≈ 1480 cm -1 . The ν(x) frequency is probably that of a C-H bend mode, as in the case of a similar vibronic component of the 2 1 A′ ← 1 1 A′ transition. No other vibrations appear to be excited in the 3 1 A′ ← 1 1 A′ electronic transition.

We note that the series of band nos. 2-15 assigned to vibronic components of the first two π-π* valence transitions are observed with various degrees of spectral resolution in several condensed-phase absorption spectra. [START_REF] Muller | Absorptions-und Phosphoreszspektren der Mono-und der Diazanaphthaline (π-π-Phosphoreszenz nach n-π-Absorption bei den Diazanaphthalinen)[END_REF][START_REF] Creṕin | A Site-Selective Spectroscopy of Naphthalene and Quinoline in TEOS/ MTEOS Xerogels[END_REF][START_REF] Zimmerman | Polarisation der Elektronenbanden von Aromaten. 3. Mitteillung: Chinolin, Isochinolin, Indol[END_REF][START_REF] Anton | Luminescence and Hydrogen Bonding in Quinoline and Isoquinoline[END_REF] In view of possible differential solvent shift effects and also effects on vibronic levels due to vibronic interactions between the n-π* and π-π* states, [START_REF] Favini | Electronic Spectra of Mono-, Di-and Tri-Azines of the Naphthalene Series[END_REF] exact correspondence between vapor-phase and condensed-phase vibrational intervals is not to be expected. Apart from the rarity of reported band energies in published condensed-phase spectra of quinoline, the resolution of our spectra is insufficient to further pursue these possible influences of solvent or matrix on quinoline vibronic level energies, apart from that on the origin band of the 1 L b transition, discussed above. The 3.9-4.630 eV featured bands overlie a broad diffuse band up to ∼5.15 eV (Figures 2 and3), whose maximum intensity, at 4.707 eV (band no. 16), has an absorption cross section of 11.43 Mb. The absorption spectrum of quinoline in a 3MP matrix at 77 K in the 3.8-4.9 eV region [START_REF] Anton | Luminescence and Hydrogen Bonding in Quinoline and Isoquinoline[END_REF] is very similar in features to our gas-phase absorption spectrum in this same spectral region, and it exhibits a broad band whose maximum is at ∼4.6 eV.

It is not immediately clear how to assign the broad 4.707 eV band. One possibility would be to reinterpret the 3.8-4.4 eV region features as all belonging to the lowest n-π* transition 1 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A″ ← 1 1 A′ and assign the broad 4.4-5.15 eV band to the π-π* transition 2 1 A′ ← 1 1 A′. However, the work of Hiraya et al., [START_REF] Hiraya | Identification of the Lowest Energy nπ* States in Gas-Phase Polycyclic Monoazines: Quinoline and Isoquinoline[END_REF] who clearly identified the location of the 1 1 A″ ← 1 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A n-π* transition, rules this out. A more reasonable assignment is that the broad diffuse band is related in some way to the second π-π* transition 3 1 A′ ← 1 1 A′, the 1 L a band. We note that the profile of this band region is similar to that of the corresponding band in solution absorption spectra of naphthalene, although the latter exhibits more pronounced overlying vibrational features [START_REF] Muller | Absorptions-und Phosphoreszspektren der Mono-und der Diazanaphthaline (π-π-Phosphoreszenz nach n-π-Absorption bei den Diazanaphthalinen)[END_REF] than does quinoline. The diffuse character of the quinoline band in the 4.7 eV region is perhaps a sign of extensive rovibronic interactions of the 3 1 A′ electronic state with a high density of rovibronic levels of lower-lying electronic states. Fluorescence excitation spectra of quinoline provide some support for the existence of these interactions, which can lead to the observed diminished fluorescence quantum yield in the excitation region of this broad diffuse absorption feature. [START_REF] Okajima | Radiationless Transitions in Gaseous Nitrogen Heterocyclics: Energy Dependence of Internal Conversion in Quinoline and Isoquinoline[END_REF][START_REF] Anton | Luminescence and Hydrogen Bonding in Quinoline and Isoquinoline[END_REF] III.1 .2 . Valence Transitions: 5 .4 -7 .5 eV. Transitions to the 4 1 A′ and Higher-Energy Electronic States. The absorption spectrum of quinoline is structured in the 5.4-7.5 eV region (Figures 2 and4-6). A group of bands starting at 5.486 eV (Bands 18-28) overlies a broad band that continues up to ∼6.8 eV. It contains some bands mainly as shoulders, the principal features being small peaks at 5.761 and 5.949 eV and shoulders at 6.022 and 6.102 eV (Table 5, Figures 2 and5). The absorption rises to a maximum at 6.218 eV with a cross section of 193.6 Mb. On the high-energy side of this broad band there are several somewhat diffuse features (Band nos. 33-37).

A few of the structured features in the 5.4-5.8 eV region are also observed in solution spectra, whose upper limit is generally ∼5.7 eV, [START_REF] Favini | Electronic Spectra of Mono-, Di-and Tri-Azines of the Naphthalene Series[END_REF][START_REF] Muller | Absorptions-und Phosphoreszspektren der Mono-und der Diazanaphthaline (π-π-Phosphoreszenz nach n-π-Absorption bei den Diazanaphthalinen)[END_REF][START_REF] Zimmerman | Polarisation der Elektronenbanden von Aromaten. 3. Mitteillung: Chinolin, Isochinolin, Indol[END_REF][START_REF] Kaito | Experimental and Theoretical Studies on the Magnetic Circular Dichroism of Azanaphthalenes. Use of the CNDO/S-CI Approximation[END_REF][START_REF] Vasǎḱ | Magnetic Circular Dichroism of Cyclic π-Electron Systems.7. Aza Analogues of Naphthalene[END_REF] and are therefore are unlikely to be Rydberg bands, since these are almost never observed in solution spectra except as much broadened bands. [START_REF] Vaida | A Note on the Elusive 1 E 2g State in the Two-Photon Spectrum of Benzene[END_REF] We assign band nos. 18-28 between 5.486 and 5.869 eV to the 1 B b band (Platt notation [START_REF] Platt | Classification of Spectra of Cata-Condensed Hydrocarbons[END_REF] ), in agreement with some previous studies, 17 that is, to the 4 1 A′ ← 1 1 A′ π-π* transition. The O 0 0 transition origin is band no. 18 at 5.486 eV and is red-shifted in solution by several hundred inverse centimeters, [START_REF] Favini | Electronic Spectra of Mono-, Di-and Tri-Azines of the Naphthalene Series[END_REF][START_REF] Muller | Absorptions-und Phosphoreszspektren der Mono-und der Diazanaphthaline (π-π-Phosphoreszenz nach n-π-Absorption bei den Diazanaphthalinen)[END_REF][START_REF] Zimmerman | Polarisation der Elektronenbanden von Aromaten. 3. Mitteillung: Chinolin, Isochinolin, Indol[END_REF] in line with the solvent polarizability parameter discussed above.

The 4 1 A′ ← 1 1 A′ transition vibronic components, assigned in band nos. 18-28, include excitation of two low-frequency vibrations, of frequencies ∼270 cm -1 (band no. 19) and ∼410 cm -1 (band no. 20), that are undoubtedly of a″ symmetry (allowed in a dipole transition of a C s symmetry molecule). Other vibronic components of this transition are assigned to three vibrational modes ν(x) ≈ 820 cm -1 , ν(y) ≈ 950 cm -1 , and ν(z) ≈ 1450 cm -1 .

The broad diffuse band whose maximum is at ∼6.218 eV overlies the minor features at 5.949 and 6.102 eV. The π-π* 5 1 A′ ← 1 1 A′, 6 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′, 7 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′, and 8 1 A′ ← 1 1 A′ transitions are expected to occur in this region (Table 6). Molecular orbital calculations by Baba and Yamazaki 38 predict π-π* transitions at 5.61 eV (f = 0.201), 5.91 eV (f = 0.165), 6.04 eV (f = 1.272), and 6.33 eV (f = 0.764). Thus, we expect several valence transitions to be observed in this spectral region.

However, this is also a region where we observe Rydberg bands. The 5.949 eV feature (band no. 29) is assigned as the origin band of the n = 3 member of the R1 Ry series, discussed in Section III.1.3 below. We note that the band nos. 18-28 that are vibronic components of the 4 1 A′ ← 1 1 A′ electronic transition (Table 5) remain reasonably sharp but are redshifted by 65 cm -1 in n-heptane solution according to our measurements of Figure 1 of the publication of Kaito and Hatano, [START_REF] Kaito | Experimental and Theoretical Studies on the Magnetic Circular Dichroism of Azanaphthalenes. Use of the CNDO/S-CI Approximation[END_REF] while the band no. 29 at 5.949 eV has a red shift of 150 cm -1 and is considerably broadened in n-heptane solution. This is consistent with band no. 29 being an n = 3 Ry band.

Furthermore, in the n-heptane solution absorption spectrum [START_REF] Kaito | Experimental and Theoretical Studies on the Magnetic Circular Dichroism of Azanaphthalenes. Use of the CNDO/S-CI Approximation[END_REF] the broad band maximum is found at 6.06 eV, redshifted by ∼1270 cm -1 with respect to the gas-phase value of 6.218 eV (band no. 32). In the pure liquid phase of quinoline studied by MacRae et al., [START_REF] Macrae | Optical Properties of Some Aromatic Liquids in the Vacuum Ultraviolet[END_REF] our measurements of their Figure 7 show that the 2 1 A′ ← 1 1 A′ transition vibronic features remain reasonably sharp, while the 4 1 A′ ← 1 1 A′ transition features are completely smoothed out, forming a broad feature whose maximum is at ∼5.41 eV. This broadening could be due to valence-Rydberg state interactions in this energy region. The broad band 5.8-6.9 eV that we assign as background to the three π-π* valence transitions 5 1 A′ ← 1 1 A′, 6 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′, and 7 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′ (Table 5), discussed below, has a maximum at ∼5.92 eV in the pure liquid phase, thus being red-shifted by ∼2400 cm -1 (300 meV) with respect to the gas phase. The 6.102 eV feature in our gas-phase absorption spectrum is assigned as the origin band of the 5 1 A′ ← 1 1 A′ valence transition, while the peak at 6.218 eV is considered to be the origin of the 6 1 A′ ← 1 1 A′ transition. These two transitions are generally calculated to have an oscillator strength of f ≈ 0.2 but are not the strongest calculated valence transitions (Table 6). The high absorption cross-section in the 6.218 eV region (193.6 Mb) must therefore be due in part to plasmon-type effects, that is, to collective modes of the π electrons that could contribute to strong absorption in the 6 eV region. [START_REF] Koch | Vacuum Ultraviolet and Electron Energy Loss Spectroscopy of Gaseous and Solid Organic Compounds[END_REF][START_REF] Bernadotte | Plasmons in Molecules[END_REF][START_REF] Krauter | Plasmons in Molecules: Microscopic Characterization Baszd on Orbital Transitions and Moment Conservation[END_REF][START_REF] Krauter | Identification of Plasmons in Molecules with Scaled Ab Initio Approaches[END_REF] These collective oscillations (plasmon-type) are many-body effects and are not dealt with in Hartree-Fock single-particle calculations. The related molecule naphthalene has a strong absorption peak at 5.89 eV 61 that has been interpreted as plasmon-type, [START_REF] Krauter | Identification of Plasmons in Molecules with Scaled Ab Initio Approaches[END_REF] reinforcing the 1 B b π-π* valence transition intensity. [START_REF] Guidez | Origin and TDDFT Benchmarking of the Plasmon Resonance in Acenes[END_REF] Vibrational components of the 5 1 A′ ← 1 1 A′ transition, if they exist, are apparently hidden in the broad background absorption. The 6 1 A′ ← 1 1 A′ valence transition has two vibrational components, with frequencies ν(x) ≈ 350 cm -1 and ν(y) ≈ 1120 cm -1 appearing in bands 6 1 A′ ← 1 1 A′ y 1 0 ; x 1 0 y 1 0 ; y 2 0 and x 1 0 y 2 0 (Table 5). The one-quantum band x 1 0 that would be expected at ∼6.261 eV is probably hidden in the intense background continuum close to the 6.218 eV maximum.

The origin of the 7 1 A′ ← 1 1 A′ transition is assigned to band no. 37 at 6.659 eV. It is expected to be a strong transition (Table 6). The absorption cross-section at that energy, enhanced by the important plasmon-type background mentioned above, is 52 Mb. This electronic transition has two vibronic components y 1 0 and y 2 0 , where ν(y) ≈ 1050 cm -1 .

The origin band of the 8 1 A′ ← 1 1 A′ π-π* transition is taken as the broad feature whose maximum is at 6.981 eV (band no. 40). It has an fwhm of ∼50 meV and thus probably contains unresolved substructure. Its breadth thus makes it difficult to pinpoint an exact origin band frequency. A four-member vibrational progression in ν(x) ≈ 900 cm -1 forms the vibronic components. The 8 1 A′ ← 1 1 A′ π-π* transition was predicted by several calculations to be in the region of 6.2 ± 0.1 eV (Table 6). Our DFT calculation value of 6.853 eV is much closer to the experimental assignment. We also assigned a few vibronic bands as belonging to the 12 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′ transition, with an origin at 7.795 eV, predicted by the DFT calculations at 7.861 eV to be the strongest of the higher-energy valence transitions. Indeed, these calculations predict a series of mainly weak higher-energy π-π* valence transitions 9 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′ to 14 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′ over a restricted energy range of 7.58-8 eV. The 9 1 A′ ← 1 1 A′, 10 1 A′ ← 1 1 A′, and 11 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ ← 1 1 A′ transitions, DFT calculated to be in the 7.24-7.7 eV region, may be present unresolved among the broad features between 7.3 and 7.7 eV (Figure 6). III.1 .3 . A Comment on the Valence-Transition Calculations. In Table 6, where we compare the calculated and observed transition energies of quinoline, we note that the unsigned difference (UD) between the DFT-calculated energies and our assigned spectral energies ranges from 0.06 to 0.66 eV, the average over the eight π-π* transitions being 0.26 eV. There have been several TD-DFT calculations of the electronic state energies of benchmark test diatomic and polyatomic molecules, [START_REF] Stratmann | An Efficient Implementation of Time-Dependent Density-Functional Theory for the Calculation of Excitation Energies of Large Molecules[END_REF][START_REF] Casida | Molecular Excitation Energies to High-Lying Bound States from Time-Dependent Density-Functional Response Theory: Characterization and Correction of the Time-Dependent Local Density Approximation[END_REF][START_REF] Furche | Adiabatic Time-Devpendent Density Functional Methods for Excited State Properties[END_REF][START_REF] Silva-Junior | Benchmarks for Electronically Excited States: Time-Dependent Density Functional Theory and Density Functional Theory Based Multireference Configuration Interaction[END_REF][START_REF] Goerigk | Computation of Accurate Excitation Energies for Large Organic Molecules with Double-Hybrid Density Functionals[END_REF][START_REF] Jacquemin | Extensive TD-DFT Benchmark: Singlet-Excited States of Organic Molecules[END_REF][START_REF] Jacquemin | On the Performances of the M06 Family of Density Functionals for Electronic Excitation Energies[END_REF][START_REF] Caricato | Electronic Transition Energies: Study of the Performance of a Large Range of Single Reference Density Functional and Wave Function Methods on Valence and Rydberg States Compared to Experiment[END_REF][START_REF] Silva-Junior | Benchmarks of Electronically Excited States: Basis Set Effects on CAPSPT2 Results[END_REF][START_REF] Isegawa | Performance of Recent and High-Performance Approximate Density Functionals for Time-Dependent Functional Theory Calculations of Valence and Rydberg Electronic Transition Energies[END_REF][START_REF] Leang | Benchmarking the Performance of Time-Dependent Density Functional Methods[END_REF][START_REF] Isegawa | Valence Excitation Energies of Alkenes, Carbonyl Compounds, and Azabenzenes by Time-Dependent Density Functional Theory: Linear Response of the Ground State Compared to Collinear and Noncollinear Spin-Flip TDDFT with the Tamm-Dancoff Approximation[END_REF] mainly limited to singlet valence excited states, but some have included triplet and Rydberg states. Most of these studies set out to compare the efficiencies of various functionals, among which the hybrid density functional B3LYP, with its 20% of Hartree-Fock exchange in the functional, [START_REF] Isegawa | Valence Excitation Energies of Alkenes, Carbonyl Compounds, and Azabenzenes by Time-Dependent Density Functional Theory: Linear Response of the Ground State Compared to Collinear and Noncollinear Spin-Flip TDDFT with the Tamm-Dancoff Approximation[END_REF] is one of the best. One typical criterion of the quality of TD-DFT calculation performance is as follows: when mean unsigned errors (MUE, where UE is equivalent to our UD) in calculated excited electronic state energies are less than 0.36 eV the TD-DFT calculations are considered to be "successful", [START_REF] Isegawa | Valence Excitation Energies of Alkenes, Carbonyl Compounds, and Azabenzenes by Time-Dependent Density Functional Theory: Linear Response of the Ground State Compared to Collinear and Noncollinear Spin-Flip TDDFT with the Tamm-Dancoff Approximation[END_REF] the range of actual UE values in a typical set of benchmark molecules being quite large, up to and greater than 1 eV. The results of our TD-TFT calculations on quinoline are thus perfectly in line with the results of benchmark calculations. [START_REF] Casida | Molecular Excitation Energies to High-Lying Bound States from Time-Dependent Density-Functional Response Theory: Characterization and Correction of the Time-Dependent Local Density Approximation[END_REF][START_REF] Furche | Adiabatic Time-Devpendent Density Functional Methods for Excited State Properties[END_REF][START_REF] Silva-Junior | Benchmarks for Electronically Excited States: Time-Dependent Density Functional Theory and Density Functional Theory Based Multireference Configuration Interaction[END_REF][START_REF] Goerigk | Computation of Accurate Excitation Energies for Large Organic Molecules with Double-Hybrid Density Functionals[END_REF][START_REF] Jacquemin | Extensive TD-DFT Benchmark: Singlet-Excited States of Organic Molecules[END_REF][START_REF] Jacquemin | On the Performances of the M06 Family of Density Functionals for Electronic Excitation Energies[END_REF][START_REF] Caricato | Electronic Transition Energies: Study of the Performance of a Large Range of Single Reference Density Functional and Wave Function Methods on Valence and Rydberg States Compared to Experiment[END_REF][START_REF] Silva-Junior | Benchmarks of Electronically Excited States: Basis Set Effects on CAPSPT2 Results[END_REF][START_REF] Isegawa | Performance of Recent and High-Performance Approximate Density Functionals for Time-Dependent Functional Theory Calculations of Valence and Rydberg Electronic Transition Energies[END_REF][START_REF] Leang | Benchmarking the Performance of Time-Dependent Density Functional Methods[END_REF][START_REF] Isegawa | Valence Excitation Energies of Alkenes, Carbonyl Compounds, and Azabenzenes by Time-Dependent Density Functional Theory: Linear Response of the Ground State Compared to Collinear and Noncollinear Spin-Flip TDDFT with the Tamm-Dancoff Approximation[END_REF] However, our calculated energies, as are the benchmark test cases, are very far from "spectroscopic accuracy"or even the 0.05 eV of "chemical accuracy". Possible sources of errors in TD-DFT calculations are discussed by Burke et al., [START_REF] Burke | Time-Dependent Density Functional Theory: Past, Present, and Future[END_REF] in particular, the adequacy of the means used to take into account the exchange-correlation potential and the associated possibility of breakdown of the local adiabatic approximation that is relevant to frequency-independent exchange-correlation functionals with which the exchangecorrelation potential adjusts instantaneously to changes in the electron density. We can add to this the problem of the adequacy of the chosen basis set. Various sources of error in TD-DFT calculations of the excited-state energies of acenes have been discussed in detail by Grimme and Parac, [START_REF] Grimme | Substantial Errors from TDDFT for the Calculation of Excited States of Large Systems[END_REF] and for heteroaromatic molecules by Prilj et al., [START_REF] Prlj | Low-Lying ππ* States of Heteroatomic Molecules: A Challenge for Excited State Methods[END_REF] in particular, the sensitivity of L b states to correlation effects, while L a states have significant double excitation character.

In Table 6 we also list the UD values for the difference between the observed and the π-π* excitation energies calculated by Baba and Yamazaki 38 by the Pariser-Parr-Pople SCF LCAO MO method plus the inclusion of configuration interaction. These have the lowest set of UD values among the various calculation studies listed in Table 6. The range of the Baba and Yamazaki UD values is from 0.06 to 0.65 eV, and the average value is 0.34 eV, ∼30% greater than for our DFT calculation. It is of interest that there is a trend to smaller UD values with increasing excitation energy in our DFT calculation, while the trend is to larger UD values in the P-P-P calculation of Baba and Yamazaki.

III.1 .4 . Rydberg and Other Transitions: 7 .1 -1 0 .7 eV. There are no previous observations of Rydberg bands in quinoline.

We assigned many of the bands observed between 7.1 and 10.7 eV to several Rydberg series that converge to various electronic states of the ion (Figure 8). We first discuss the energies of the ion states.

The initial ionization energy of quinoline has been measured mainly by He I photoelectron spectroscopy. Reported values are 8.67 eV, [START_REF] Eland | Inner Ionization Potentials of Aromatic Compounds[END_REF] 8.62 eV, 27,77-79 8.65 eV, [START_REF] Ahmed | Correlation of Experimental Ionization Potentials with Calculated Molecular Energies[END_REF] 8.61 ± 0.02 eV, [START_REF] Bouwman | Dissociative Photoionization of Quinoline and Isoquinoline[END_REF] as well as ion yield curve onset values of 8.62 ± 0.01 eV 81 and 8.57 ± 0.05 eV. [START_REF] Leach | VUV Dissociative Photoionization of Quinoline in the 7-26 eV Photon Energy Range[END_REF] Reported successive ionization energies are 9.18, 9.39, 10.57, 11.3, 11.5, 11.9, and 12.4 eV. [START_REF] Moomaw | Strained Heterocyclic Systems.10. Photoelectron Spectra and Theoretical Studies of Bonding in Strained Quinolines[END_REF][START_REF] Brogli | Photoelectron Spektra of Azabenzenes and Azanaphthalenes: A Reinvestigation of Azanaphthalenes by High-Resolution Photoelectron Spectroscopy[END_REF][START_REF] Dryza | Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline and Quinoline[END_REF] We will refer to the ground doublet electronic state of quinoline as D 0 and to the successive excited states as D 1 -D 7 .

As a result of our observation of an extensive R1 series of Rydberg bands, from n = 3 to n = 16, converging on the ion ground state, we were able to refine the value of the ionization energy. In establishing the R1 series (see below) we explored the following trial ionization energies (IEs) over the range of IE = 8.620-8.630 eV at intervals of 0.0025 eV. On the basis of the simple assumption, usually made, [START_REF] Hochmann | Chemical Spectroscopy and Photochemistry in the Vacuum-Ultraviolet[END_REF] that the quantum defect δ is approximately constant for a given progression in n, we found that the most consistent set of δ values over the whole series was obtained with IE = 8.628 eV. We adopted this as the adiabatic ionization energy of quinoline to the D 0 ground state.

Determination of the ionization energies to the excited ion states was accomplished using transition energy data from the electronic spectra of gas-phase quinoline-Ar complexes observed by Dryza et al. [START_REF] Dryza | Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline and Quinoline[END_REF] They were able to estimate the D 3 ← D 0 and D 4 ← D 0 electronic transition energies of the bare ion as 1.995 and 2.2727 eV, respectively. On the basis of DFT calculations they also predicted the D 1 ← D 0 and D 2 ← D 0 transition energies to be 0.718 and 0.916 eV, respectively.

Using this information, we list the first five ionization energies of quinoline as 8.628 eV (D 0 ); (9.346 eV), 9.16 eV, [START_REF] Brogli | Photoelectron Spektra of Azabenzenes and Azanaphthalenes: A Reinvestigation of Azanaphthalenes by High-Resolution Photoelectron Spectroscopy[END_REF] (D 1 ); 9.25 ± 0.05 eV, [START_REF] Brogli | Photoelectron Spektra of Azabenzenes and Azanaphthalenes: A Reinvestigation of Azanaphthalenes by High-Resolution Photoelectron Spectroscopy[END_REF] The R1 Ry series converges on the D 0 doublet ground state of the quinoline cation (Table 5, Figure 2). Our analysis is based on the equation for the energy E(n) of the nth member of a Rydberg series: E(n) = IE -R/(nδ) [START_REF] Mattioda | Infrared Spectroscopy of Matrix-Isolated Polycyclic Aromatic Compounds and Their Ions. 6. Polycyclic Aromatic Nitrogen Heterocycles[END_REF] , where IE (quinoline) = 8.628 eV, R = 13.606 eV is the Rydberg constant, and δ is the quantum defect. The first members of the R1 series are n = 3 and are assigned, respectively, to band no. 29 (R1 n = 3, δ = 0.746), which occurs in a spectral region dominated by π-π* valence transitions. The succeeding members n = 4,5,6,... (Table 5) have higher quantum defects, of the order of δ = 1.0 ± 0.1. This difference in quantum defect values with respect to n = 3 is understandable in that in the n = 3 Ry state the radius of the Rydberg orbital is similar to that of the ion core, leading to some coupling with the π orbitals and resulting in deviations from the H atom model that lies behind the formula for E(n). A similar difference between quantum defects for n = 3 and n ≥ 4 Ry levels is observed for naphthalene, the hydrocarbon parent of quinoline. For naphthalene, the n = 3 members of the lowest observed Rydberg series have values δ ≈ 0.68, [START_REF] Angus | The Lowest Free Molecule Rydberg Transition of Naphthalene[END_REF] while for n ≥ 4 Ry levels the quantum defects δ ≈ 0.85. [START_REF] Koch | The Vacuum Ultraviolet Spectrum of Naphthalene Vapour for Photon Energies from 5 to 30 eV[END_REF] Members of the R1 series were assigned up to n = 16, close to the ionization limit. The limited band resolution is probably responsible for the spread of quantum defect values around δ ≈ 1 for the highest n values of the series. The lower value δ ≈ 0.871 for n = 5 may be due to interactions with the 12 [START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′ valence state in this energy region. The generally smaller quantum defect values for the lower members of a Rydberg series result from a greater effect of the core potential as compared with the higher n values. From the overall values of the quantum defect we assign the R1 Ry series as a nanosecond series arising from ejection of an electron from the HOMO π -1 orbital (Table 7).

This Rydberg series has vibrational components (Table 5). These involve ν(x) 540 ± 40 cm -1 , ν(y) 800 ± 30 cm -1 , and ν(z) ≈ 1300 cm -1 . The ν(x) ≈ 540 cm -1 mode is probably related to the ν(29) = 522 cm -1 ring deformation mode of neutral ground-state quinoline (Table 2). The infrared multiphoton dissociation (IRMPD) spectrum of the quinoline ion ground state, measured in the 600-1600 cm -1 region, [START_REF] Alvaro Galue | Gas-Phase Infrared Spectra of Cationized Nitrogen-Substituted Polycyclic Aromatic Hydrocarbons[END_REF] has a strong broad band with two components at 700-900 cm -1 and other overlapping broad strong bands centered at 1170 and 1450 cm -1 . These are the regions of our ν(y) ≈ 800 cm -1 and ν(z) ≈ 1300 cm -1 R1 series vibrational components. We also note that, in the HeI photoelectron spectrum of quinoline, the first band (first ionization) has a relatively broad vibrational component whose frequency is of the order of 1300 cm -1 . [START_REF] Moomaw | Strained Heterocyclic Systems.10. Photoelectron Spectra and Theoretical Studies of Bonding in Strained Quinolines[END_REF] It is reasonable to consider that ν(y) ≈ 800 cm -1 and ν(z) ≈ 1300 cm -1 correspond, respectively, to ν(27) = 760 cm -1 and ν(14) = 1392 cm -1 in the neutral ground state, respectively, ring deformation and C-C stretch modes.

A second set of Rydberg bands converging to the ion ground state D 0 at 8.628 eV was observed for n = 3-7 levels, with quantum defect δ ≈ 0.67 (Table 5, Figure 2). No vibrational components were observed for this R2 series. This Rydberg series, which also arises from ejection of an electron from the HOMO π -1 orbital, was assigned as an np series (Table 7).

The strong underlying π-π* transition continuum in the 8 eV region (Figure 7) has an intensity maximum at ∼8.1 eV (σ abs = 65 Mb) that reaches a minimum at 8.66 eV, just above the IE = 8.628 eV value that we adopted as the ionization energy of quinoline. The absorption curve then develops another small broad continuum that rises to a maximum at 8.81 eV (σ abs = 39 Mb) and a minimum at ∼9.1 eV, followed by a rise to a maximum at 9.77 eV (σ abs = 52 Mb). The minimum at 8.66 eV reflects the onset of the first ionization of quinoline, while the 9.1 eV minimum reflects the onset of higher-energy ionization channels whose reported energies are IE(D 1 ) = 9.16 eV and IE(D 2 ) = 9.25 ± 0.05 eV, [START_REF] Brogli | Photoelectron Spektra of Azabenzenes and Azanaphthalenes: A Reinvestigation of Azanaphthalenes by High-Resolution Photoelectron Spectroscopy[END_REF] discussed above. Attempts to find corresponding Rydberg series converging to the D 1 and D 2 electronic states were unsuccessful.

We were able to assign three Rydberg series of bands that converge to the D 3 excited state of the quinoline ion at 10.623 eV. Bands n = 3-9 of the R3 series are listed in Table 5. They are weaker than those of the corresponding n term bands of the R1 series. The quantum defects in the R3 series are δ ≈ 0.98, so that we assign this series as ns-type, arising from ejection of an electron from the HOMO-3 orbital (Table 7). No vibrational components were recognized and indeed were not expected, judging from the profile of the HeI photoelectron spectrum in this ion state region [START_REF] Brogli | Photoelectron Spektra of Azabenzenes and Azanaphthalenes: A Reinvestigation of Azanaphthalenes by High-Resolution Photoelectron Spectroscopy[END_REF] (see also below).

The second set of Rydberg bands converging to the D 3 ion state is limited to four O 0 0 members n = 3-6 of the R4 series (Table 5). The quantum defect is δ ≈ 0.66, typical of an np 1type series (Table 7). The third series R5 has six components, n = 3-8, with a quantum defect δ ≈ 0.28, indicating that it is np 2 -type (Table 7). Some of the peaks in the 8-10.7 eV region (Figure 8) could be assigned to three further Rydberg series R6, R7, and R8 that converge to the D 4 excited electronic state of the cation at 11.355 eV (Table 5, Figure 2), which is formed by ejection of an electron from the HOMO-4 orbital. The series R6 consists of three assigned members, n = 3-5. The quantum defects of these bands are δ ≈ 0.98, with the series assigned as ns-type. The R7 Ry series (Table 5, Figure 2) has three assigned members, n = 3-5, δ ≈ 0.72, while the R8 series has two members, n = 3, 4, with quantum defects δ ≈ 0.25. Higher members of these last two fragmentary series, respectively considered as being of np 1 -type and np 2 -type (Table 7), are required to verify the assignments, but their Rydberg levels n > 5 are estimated to be beyond our 10.7 eV energy measurement limit.

We remark that the D 3 ← D 0 electronic transition of the quinoline cation, observed by absorption spectra using photodissociation spectroscopy, [START_REF] Dryza | Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline and Quinoline[END_REF] contains a number of well- resolved vibrational components; the weaker D 4 ← D 0 transition appears to be limited to the O 0 0 band. We would expect Rydberg vibrational components to mimic those in direct photoionization to the cation electronic levels. This is not necessarily the case for the cation transition vibrational components because of a possible difference in the Franck-Condon factors operative in the cation absorption transition and in the process of photoionization of the neutral molecule. Indeed, in the successive members of our quinoline Rydberg series that converge to the D 3 excited state of the ion we did not observe consistent consecutive features that could correspond to the vibrational components occurring in the cation absorption spectra. A comparison of the Dryza et al. cation spectra of quinoline [START_REF] Dryza | Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline and Quinoline[END_REF] with HeI photoelectron spectral bands involving ionization to the D 3 excited states of the cations [START_REF] Eland | Inner Ionization Potentials of Aromatic Compounds[END_REF][START_REF] Brogli | Photoelectron Spektra of Azabenzenes and Azanaphthalenes: A Reinvestigation of Azanaphthalenes by High-Resolution Photoelectron Spectroscopy[END_REF] appears to support the existence of a difference in the relevant Franck-Condon factors. A similar situation holds for the analogous relevant spectra of naphthalene. [START_REF] Koch | The Vacuum Ultraviolet Spectrum of Naphthalene Vapour for Photon Energies from 5 to 30 eV[END_REF][START_REF] Eland | Inner Ionization Potentials of Aromatic Compounds[END_REF][START_REF] Brogli | Photoelectron Spektra of Azabenzenes and Azanaphthalenes: A Reinvestigation of Azanaphthalenes by High-Resolution Photoelectron Spectroscopy[END_REF][START_REF] Dryza | Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline and Quinoline[END_REF][START_REF] Mayer | Threshold Photoelectron Study of Naphthalene, Anthracene, Pyrene, 1,2-Dihydronaphthalene, and 9,10-Dihydroanthracene[END_REF] However, higher-resolution PES spectra and/or calculation of the respective Franck-Condon factors are required to fully justify this interpretation.

The features between 9.0 and 10.7 eV overlie an important background continuum that reaches a quasi-constant cross section σ abs ≈ 52 Mb between 9.7 and 10.1 eV and then rises to another quasi constant cross section σ abs ≈ 70 Mb between 10.38 and 10.7 eV, the high-energy end of the measured absorption spectrum. The origin of the background continua requires further theoretical and experimental investigation. We remark that other valence transitions, such as π-σ*, σ-π*, and σ-σ*, could be active besides the known π-π* and n-π* transitions and be responsible for an intense background that interferes little with the Rydberg and valence states.

We also examined whether some of the small peaks in the 9.77 to 11 eV region could be due to Rydberg transitions of a water impurity. However, we rejected this water conjecture after careful comparison of our spectrum with published absorption spectra and assignments of H 2 O in this spectral region. [START_REF] Bell | The spectra of H 2 O and D 2 O in the vacuum ultraviolet[END_REF][START_REF] Yoshino | Absorption Cross Section Measurements of Water Vapor in the Wavelength Region 120 to 188 nm[END_REF][START_REF] Watanabe | Absorption Coefficients of Water Vapor in the Vacuum Ultraviolet[END_REF][START_REF] Gurtler | Rydberg Series in the Absorption Spectra of H 2 O and D 2 O in the Vacuum Ultraviolet[END_REF][START_REF] Chan | The electronic spectrum of water in the discrete and continuum regions. Absolute optical oscillator strengths for photoabsorption (6-200 eV)[END_REF] We were also assured that the same spectral features in the 9.77-11 eV region are not due to noise by the fact that they are exactly reproduced in a series of successive VUV absorption runs.

III.1 .5 . Comparison with the Absorption Spectrum of Liquid Quinoline. It is of interest to examine the absorption spectrum of liquid quinoline in the VUV region and to compare it with our gas-phase observations. MacRae et al. [START_REF] Macrae | Optical Properties of Some Aromatic Liquids in the Vacuum Ultraviolet[END_REF] studied the optical properties of liquid quinoline by reflectance and transmission measurements in the 2-10.6 eV spectral region. They determined absorption cross sections over the 3.5-10.6 eV range and compared their spectra with published solution spectra measured between 3.5 and 5.5 eV.

Our gas-phase spectrum over the 3.5-10.7 eV range has many general similarities to the liquid-phase spectrum, but it shows more detailed structure and much better-resolved bands, where the liquid-phase bands are broad, as is the case for all bands above 4.2 eV. As expected, none of our assigned Rydberg band features are observed in the liquid-phase spectrum.

In the liquid phase the maximum absorption is at ∼6 eV with a cross section of ∼80 Mb, whereas we measure 193.6 Mb at our 6.218 eV maximum. This modification indicates a difference, between the liquid and gas phases, in the collective electron oscillations contributing to the absorption in this energy region marked by plasmon effects. The liquid-phase broad band between 6.9 and 8.8 eV corresponds to the more restricted background continuum between 7.5 and 8.6 eV in our gas-phase spectrum. However, the liquid-phase absorption cross-section maximum at 7.84 eV has a cross section of ∼60 Mb similar to that of our gas-phase maximum in this spectral region, σ abs = 62.15 Mb. Furthermore, the absorption cross sections at 10.5 eV are similar in both liquid and gas, where σ abs ≈ 70 Mb.

IV. CONCLUSION

Quinoline absorption spectra were measured in the gas phase between 3.6 and 10.7 eV using the Aarhus synchrotron radiation facility photon source ASTRID2. A large number of sharp and broad spectral features was observed. These observations provide new information beyond those of previous studies that were mainly performed in solution and limited to an upper energy of ∼5.6 eV. TD-DFT calculations of quinoline of its ground state properties such as geometry, rotational constants, dipole moment, and vibrational frequencies agree well with experimental observations. The results of previous P-P-P quantum-mechanical computations of the valence-state energy levels and optical transition strengths, along with the results of our TD-DFT calculations of these quantities, were used to assign eight π-π* singlet m 1 A′ ← 1 1 A′ valence electronic transitions of quinoline, along with their vibrational components. Only a small number of these electronic transitions were previously observed or assigned. The relative quality and trends of the P-P-P and DFT calculation results is discussed. Both are far from spectroscopic or even chemical accuracy but have proved useful in our assignments of the valence transitions. The n-π* transitions of these two compounds were too weak to be observed, as confirmed by our DFT calculations. It is suggested that some broad features, in particular, the intense broad band whose maximum is at 6.218 eV, may have plasmon-type collective π electron modes as important contributing components to their intensities.

Rydberg bands of quinoline were also observed for the first time and are analyzed into series converging to ground and to excited cation electronic states. Eight Rydberg series were assigned, two of which, R1 and R2 and their vibrational components, converge to the D 0 ion ground state. The extensive number of members of the R1 series enabled us to determine a value of 8.628 eV for the initial ionization energy of quinoline, a value more precise than previously published. The more limited third, fourth, and fifth Rydberg series, R3, R4, and R5, converge to the D 3 ion excited state at 10.623 eV, while the sixth, seventh, and eighth series, R6, R7, and R8, converge to the D 4 ion excited state at 11.355 eV.

A comparison of our gas-phase quinoline absorption spectrum with that measured for liquid quinoline in the 3.5-10.5 eV region [START_REF] Macrae | Optical Properties of Some Aromatic Liquids in the Vacuum Ultraviolet[END_REF] shows many general similarities in the valence-state region and the expected absence of Rydberg bands in the liquid phase.

Of the 137 measured features in our absorption spectrum 39 (28%) are not assigned. These nonassigned bands are mainly in the high-energy region. They are possibly higher-valence transitions or, more likely, Rydberg features to the numerous highly excited ion states, to and even beyond the D 4 level. We require more extended spectral measurements, up at least to 12 eV, to check these possibilities.

Finally we note that our spectral absorption data include absorption cross-section measurements in the VUV that can provide useful new information for theoretical modeling of photochemical processes involving quinoline in planetary atmospheres and in the interstellar medium. Extensive spectroscopic searches for quinoline in the 75-158 GHz frequency range have been made toward the circumstellar envelopes of carbon-rich stars. [START_REF] Charnley | Astronomical Searches for Nitrogen Heterocycles[END_REF] No positive results were obtained, but upper limits on the column densities were derived. The target stars were IRC + 10216, CRL 618, and CRL 2688. The latter two stars are protoplanetary nebulae in which molecules in the outflowing circumstellar envelope receive intense UV radiation from the star. In IRC + 10216, an AGB star, the inner dusty envelope is less subject to destructive UV irradiation, but molecules in the outward flow would enter regions of increasing UV flux and be subject to photodisociation.

To be more useful to astrophysical problems, our data need to be amplified by measurement of photoionization quantum yields of quinoline, going beyond rule-of-thumb estimations of energy-dependent ionization quantum yields. [START_REF] Jochims | Photoionization Quantum Yields of Polycyclic Hydrocarbons[END_REF][START_REF] Page | Hydrogenation and Charge States of PAHS in [Diffuse Clouds. I. Development of a Model[END_REF] This is of particular interest to assess the importance of photophysical and photochemical processes involving superexcited electronic states of the neutral molecule as a function of absorbed energy. [START_REF] Hatano | Interaction of VUV Photons with Molecules. Spectroscopy and Dynamics of Molecular Superexcited States[END_REF] As an example, but using a rule-of-thumb method, [START_REF] Jochims | Photoionization Quantum Yields of Polycyclic Hydrocarbons[END_REF] we estimate the quantum yield of ionization of quinoline to be γ i (13.6 eV) = 0.54 at the astrophysical HI region energy limit of 13.6 eV, so that ∼45% of the absorbed photon energy at 13.6 eV is retained for neutral molecule relaxation processes, including molecular dissociation. At an incident photon energy of 10.7 eV, the upper energy limit of our absorption spectral measurements, we estimate that ∼75% of the absorbed photon energy relaxes by nonionization processes.

Notes

The authors declare no competing financial interest.

Figure 1 .

 1 Figure 1 . Calculated geometry of quinoline. Bond distances (Å) and angles (deg) calculated by a TD-DFT method.

I

  . Quinoline Rotational Constants: (a) DFT-calculated rotational constants (present study): A = 3.140 8386 GHz, B = 1.265 7855 GHz, C = 0.902 1936 GHz (b) microwave spectroscopy (Kisiel et al. 26 ): A = 3.145 533 013 GHz, B = 1.271 577 972 GHz, C = 0.905 739 406 GHz (c) microwave and FIR spectroscopy (Pirali et al. 28 ): A = 3.145 533 064 GHz, B = 1.271 578 102 GHz, C = 0.905 739 476 GHz II. Quinoline Dipole Moment: (a) DFT-calculated dipole moment: 2.2254 D (present study) (b) gas-phase dipole moment from polarization measurement (Buckingham et al.

Figure 2 .

 2 Figure 2 . Quinoline absorption spectrum 3.6-10.7 eV. Bands of the Rydberg series R1-R8 are indicated. The O 0 0 origin bands of the successive π-π* valence transitions m 1 A′ ← 1 1 A′ (Table 5) are indicated as 2 1 A′•••12 1 A′. Vibrational components listed in Table 5 are not indicated, for clarity in the figure.

  modified intermediate neglect of differential overlap (INDO) method in their SCF LCAO MO calculations (Table

Figure 3 .

 3 Figure 3 . Quinoline absorption spectrum 3.5-5.0 eV. Band numbers are pinpointed.

a

  sh = shoulder. Vibrational modes x, y, and z are specific to the various m 1 A′ ← 1 1 A′ valence transitions and to the Rydberg transitions.

Figure 4 .

 4 Figure 4 . Quinoline absorption spectrum 4.5-5.8 eV. Band numbers are pinpointed.

Figure 5 .

 5 Figure 5 . Quinoline absorption spectrum 5.5-6.2 eV. Band numbers are pinpointed.

Figure 6 .

 6 Figure 6 . Quinoline absorption spectrum 6.5-7.8 eV. Band numbers are pinpointed.

Figure 7 .

 7 Figure 7 . Quinoline absorption spectrum 7.5-8.7 eV. Band numbers are pinpointed.

  (9.544 eV) (D 2 ); 10.623 eV (D 3 ), and 11.355 eV (D 4 ), the D 1 and D 2 values (in brackets) being based on DFT calculations. The D 0 , D 1 , D 3 , and D 4 levels arise, respectively, from (HOMO)π -1 , (HOMO-1)π -1 , (HOMO-3)π -1 , and (HOMO-4)π -1 electron ejections, while the D 2 level is formed by electron ejection from (HOMO-2)n -1 , this lone pair orbital n being of σ-type (HOMO = highest occupied molecular orbital).[START_REF] Brogli | Photoelectron Spektra of Azabenzenes and Azanaphthalenes: A Reinvestigation of Azanaphthalenes by High-Resolution Photoelectron Spectroscopy[END_REF]

Figure 8 .

 8 Figure 8 . Quinoline absorption spectrum 8.5-10.7 eV. Band numbers are pinpointed.

  33-(0)145077561. E-mail: Sydney.Leach@obspm.fr.

Table 1 .

 1 Calculated and Experimental Physical Properties of Quinoline

  Our DFT study included calculations of the ground-state harmonic and anharmonic vibrational frequencies of quinoline. The results on the 31 a′ symmetry and 14 a″ vibrational modes, compared with the experimental values of Wait and McNerney 32 and with other calculations of quinoline vibrational frequencies, are presented in Tables

30 ): 2.27 ± 0.05 D (c) gas-phase dipole moment from Stark effect measurement (Kisiel et al. 26 ): 2.0197 D methods has recently been listed and discussed by Ebenso et al. 31 II.2 .2 . Ground-State Vibrational Frequencies.

Table 3 .

 3 Quinoline Vibrational Frequencies (cm -1 ): Anharmonic Frequency DFT Calculations cf. Observed Values

	vibrational mode 32	observed 32	B97-1 6-311+G(d,p) B97-1 6-311G(d,p) B97-1 6-311G(d,p) 29 B3LYP 6-311+G(d,p) B3LYP 6-31+G(d,p)
	1 a′	3085	3077	3080	3064	3067
	2 a′	3056	3057	3058	3055	3075
	3 a′	3056	3067	3052	3060	3095
	4 a′	3036	3038	3040	3044	3052
	5 a′	3015	3033	3039	3041	3055
	6 a′	3005	3000	3010	3007	3021
	7 a′	2982	3012	3000	3011	3031
	8 a′ 1013	1012	1013	1013	1020
	25 a′	956	933	934	934	937
	26 a′	785	814	814	814	818
	27 a′	760	754	755	755	760
	28 a′	612; 611 29	614	614	614	618
	29 a′	522	521	521	521	524
	30 a′	(505)	519	520	520	522
	31 a′	380; 375 29	375	375	375	379
	32 a″	986	978	977	977	981
	33 a″	971	981	978	978	980
	34 a″	940	953	952	951	954
	35 a″	868	950	948	949	953
	36 a″	850	872	868	866	898
	37 a″	806	807	807	808	814
	38 a″	786	783	788	787	797
	39 a″	741	733	734	735	733
	40 a″	629; 628 29	628	633	631	643
	41 a″	479; 476 29	480	481	480	485
	42 a″	472	468	469	467	482
	43 a″	393; 389 29	391	493	392	395
	44 a″	192; 178 28	176	179	178	180
	45 a″	178; 168 28	170	172	170

Table 4 .

 4 Quinoline. DFT-Calculated Singlet Transition Energies and Oscillator Strengths

	transition	transition energy, eV	oscillator strength, f
	1A″ ← 1A′	4.6228	0.0023
	2A′ ← 1A′	4.6484	0.0274
	3A′ ← 1A′	4.7312	0.0622
	2A″ ← 1A′	5.6923	0.0000
	4A′ ← 1A′	6.0226	0.9655
	5A′ ← 1A′	6.2419	0.0489
	3A″ ← 1A′	6.3132	0.0000
	6A′ ← 1A′	6.4344	0.1934
	7A′ ← 1A′	6.5980	0.2540
	4A″ ← 1A′	6.6941	0.0024
	5A″ ← 1A′	6.8215	0.0278
	6A″ ← 1A′	6.8419	0.0076
	8A′ ← 1A′	6.8529	0.1008
	7A″ ← 1A′	6.9287	0.0002
	8A″ ← 1A′	7.2017	0.0002
	9A′ ← 1A′	7.2399	0.0378
	9A″ ← 1A′	7.2866	0.0004
	10A″ ← 1A′	7.3051	0.0011
	11A″ ← 1A′	7.4243	0.0072
	12A″ ← 1A′	7.4698	0.0056
	10A′ ← 1A′	7.5841	0.0006
	13A″ ← 1A′	7.5996	0.0048
	14A″ ← 1A′	7.6699	0.0008
	11A′ ← 1A′	7.7013	0.0035
	15A″ ← 1A′	7.7300	0.0020
	12A′ ← 1A′	7.8613	0.0464
	13A′ ← 1A′	7.9459	0.0085
	16A″ ← 1A′	7.9466	0.0003
	14A′ ← 1A′	7.9979	0.0016
	17A″ ← 1A′	8.1113	0.0012
	18A″ ← 1A′	8.1521	0.0068
	19A″ ← 1A′	8.1903	0.0002
	20A″ ← 1A′	8.2142	0.0001

Table 5 .

 5 Quinoline Gas-Phase Absorption Spectrum: Band Energies and Assignments a

	band no.	energy, eV	energy, cm -1	assignment: vibrational frequencies in cm -1	quantum defect of Rydberg series O 0 0 bands	band no.	energy, eV	energy, cm -1	assignment: vibrational frequencies in cm -1	quantum defect of 0 Rydberg series O 0 bands
	1	3.984	32 134 -56 see text							51	7.546	60 864 R1 (n = 4) y 2	0 z 1	0
	2	3.991	32 190 2 1 A′ ← 1 1 A′ O 0	0				52	7.609	61 638 R3 (n = 3) O 0	0	R3 δ = 0.876
	3	3.996	32 232 + 42 see text							53	7.653	61 728
	4	4.065 (sh) 32 788								54	7.795	62 873 12 1 A′ ← 1 1 A′ O 0	0
	5	4.080	32 906 2 1 A′ ← 1 1 A′ x 1	0					55	7.815 (sh) 63 032
	6	4.120	33 228 2 1 A′ ← 1 1 A′ y 1	0					56	7.830	63 151 R1 (n = 5) O 0	0	R1 δ = 0.871
	7 8 9	4.125 4.163 4.165	33 272 2 1 A′ ← 1 1 A′ y 1 see text 33 573 2 1 A′ ← 1 1 A′ z 1 0 0 + 44 33 590 2 1 A′ ← 1 1 A′ x 2 0		57 58 59	7.852 7.869 (sh) 63 467 63 331 12 1 A′ ← 1 1 A′ x 1 7.897 63 694 R2 (n = 5) O 0 0 ; R1 0 0 (n = 5) x 1	R2 δ = 0.685
	10 11 12 13 14 15 16 17 18 19 20	4.250 4.295 4.343 4.441 4.527 4.630 4.707 4.868 (sh) 39 263 34 282 2 1 A′ ← 1 1 A′ x 1 2 1 A′ ← 1 1 A′ y 2 0 z 1 0 34 638 2 1 A′ ← 1 1 A′ y 1 0 z 1 0 ; 0 35 026 2 1 A′ ← 1 1 A′ z 2 0 ; 2 1 A′ ← 1 1 A′ x 2 0 z 1 0 35 819 3 1 A′ ← 1 1 A′ O 0 0 36 513 3 1 A′ ← 1 1 A′ x 1 0 37 343 3 1 A′ ← 1 1 A′ z 1 0 37 965 maximum of broad diffuse background 5.486 44 247 4 1 A′ ← 1 1 A′ O 0 0 5.519 44 511 4 1 A′ ← 1 1 A′ O 0 0 + 264 (264 = a″ vib) see text) 5.538 44 667 4 1 A′ ← 1 1 A′ O 0 0 + 420 (420 = (a″ vib) see text)		60 61 62 63 64 65 66 67 68 69 70 71 72 73	7.917 7.955 7.981 7.996 8.025 8.043 8.075 8.080 8.097 8.109 8.125 8.149 8.177 8.192	63 855 12 1 A′ ← 1 1 A′ x 2 64 164 R1 (n = 5) x 2 0 64 371 R1 (n = 5) z 1 0 64 495 64 725 R6 (n = 3) O 0 0 ; R1 0 (n = 5) x 3 0 64 872 65 126 65 168 R1 (n = 6) O 0 0 65 306 65 402 65 531 65 726 R2 (n = 6) O 0 0 ; R1 (n = 6) x 1 0 65 952 R4 (n = 3) O 0 0 ; R1 (n = 6) y 1 0 66 072	R6 δ = 0.979 R1 δ = 1.018 R2 δ = 0.670 R4 δ = 0.642
	21	5.586	45 054 4 1 A′ ← 1 1 A′ x 1	0					74	8.208	66 203
	22 23	5.603 5.669	45 187 4 1 A′ ← 1 1 A′ y 1 45 724 4 1 A′ ← 1 1 A′ z 1 0 0					75 76	8.246 8.263	66 511 R1 (n = 7) O 0 66 644	0	R1 δ = 1.029
	24 25	5.693 5.724	45 914 4 1 A′ ← 1 1 A′ x 2 46 168 4 1 A′ ← 1 1 A′ y 2 0 0					77 78	8.285 8.304	66 822 R2 (n = 7) O 0 66 979	0	R2 δ = 0.670
	26	5.761	46 468 4 1 A′ ← 1 1 A′ x 1	0 z 1	0		79	8.335	67 227
	27 28 29 30	5.791 5.869 5.949 6.022 (sh) 48 570 R1 (n = 3) x 1 46 707 4 1 A′ ← 1 1 A′ x 3 47 336 4 1 A′ ← 1 1 A′ x 2 47 984 R1 (n = 3) O 0 0 0 0 z 1 0 ; R2 0 (n = 3) O 0 0	R1 δ = 0.746 R2 δ = 0.715	80 81 82 83	8.346 8.360 8.414 8.423	67 317 R1 (n = 8) O 0 ; R1 (n = 7) y 1 0 67 431 67 866 R1 (n = 9) O 0 0 67 936	R1 δ = 1.050 R1 δ = 1.021
	31 32 33 34 35 36 37 38 39	6.102 (sh) 49 220 5 1 A′ ← 1 1 A′ O 0 6.218 50 150 6 1 A′ ← 1 1 A′ O 0 6.357 (sh) 51 272 6 1 A′ ← 1 1 A′ y 1 0 6.400 51 620 6 1 A′ ← 1 1 A′ x 1 0 y 1 0 0 6.495 52 384 6 1 A′ ← 1 1 A′ y 2 0 6.538 (sh) 52 732 6 1 A′ ← 1 1 A′ x 1 0 y 2 6.659 (sh) 53 708 7 1 A′ ← 1 1 A′ O 0 0 6.792 54 781 7 1 A′ ← 1 1 A′ y 1 0 6.909 55 725 7 1 A′ ← 1 1 A′ y 2 0	0 0		84 85 86 87 88 89 90 91 92	8.440 8.460 8.492 8.515 8.530 8.548 8.560 8.568 8.583	68 073 R1 (n = 8) y 1 68 236 R1 (n = 10) O 0 0 68 493 R1 (n = 11) O 0 68 681 R1 (n = 12) O 0 68 799 R1 (n = 13) O 0 68 944 R1 (n = 14) O 0 69 037 R1 (n = 15) O 0 69 108 R1 (n = 16) O 0 69 228	0 0 0 0 0 0 0	R1 δ = 0.995 R1 δ = 0.994 R1 δ = 1.008 R1 δ = 1.217 R1 δ = 0.983 R1 δ = 0.907 R1 δ = 0.891
	40 41 42 43 44 45 46 47 48 49 50	6.981 7.083 7.177 7.204 (sh) 58 105 8 1 A′ ← 1 1 A′ x 2 56 306 8 1 A′ ← 1 1 A′ O 0 broad band ΔE ≈ 0 50 meV 57 126 8 1 A′ ← 1 1 A′ x 1 0 57 887 R1 (n = 4) O 0 0 0 7.242 (sh) 58 407 R1 (n = 4) x 1 0 7.274 58 668 R1 (n = 4) y 1 0 7.335 59 160 8 1 A′ ← 1 1 A′ x 3 0 7.345 59 241 R1 (n = 4) z 1 0 7.373 59 467 R1 (n = 4) y 2 0 7.403 59 709 R2 (n = 4) O 0 0 7.449 60 077 R1 (n = 4) y 1 0 z 1 0 ; 8 1 A ′ ← 1 1 A′ x 4 0	R1 δ = 0.938 R2 δ = 0.871	93 94 95 96 97 98 99 100 8.840 8.607 8.616 8.631 8.652 8.689 8.741 8.803 101 8.913 102 9.147 103 9.273 104 9.340 105 9.414 (sh) 75 929 R4 (n = 4) O 0 69 420 69 492 69 613 69 784 70 081 70 497 R7 (n = 3) O 0 70 997 R7 (n = 3) x 1 0 71 301 R5 (n = 3) O 0 71 890 73 774 R3 (n = 4) O 0 74 794 75 329	0 0 0 0	R7 δ = 0.719 R5 δ = 0.239 R3 δ = 0.966

Table 5 . continued

 5

	band no.	energy, eV	energy, cm -1	assignment: vibrational frequencies in cm -1	quantum defect of 0 Rydberg series O 0 bands
	106 9.468 (sh) 76 374
	107 9.563 (sh) 77 130
	108 9.619	77 579 R5 (n = 4) O 0	0	R5 δ = 0.319
	109 9.679	78 064 R8 (n = 3) O 0	0	R8 δ = 0.151
	110 9.717	78 369
	111 9.

Table 6 .

 6 Quinoline π-π* m 1 A′← 1[START_REF] Landera | Mechanisms of Formation of Nitrogen-Containing Polycyclic Aromatic Compounds in Low-Temperature Environments of Planetary Atmospheres: A Theoretical Study[END_REF] A′Singlet Transitions: Calculated Energies (eV) and Oscillator Strengths

										observed	DFT -obs	Baba-obs
	A′state	Fav 17	Mat 43	Tin 40	Nish 39	Baba 38	Rid 41	Wag 42	DFT present study	transition energy	unsigned (UD)	unsigned (UD)
	2 1 L a		4.231	4.00 0.026	3.97 0.052	4.09 0.060	4.14 0.04	4.07 0.04	4.6484 0.0274	3.991	0.657	0.10
	3 1 L b	4.42 0.076	4.270	4.527 0.163	4.47 0.170	4.32 0.207	4.54 0.16	4.86 0.19	4.7312 0.0622	4.441	0.29	0.12
	4 1 B b	5.546 0.005	5.813	5.460 0.753	5.29 0.583	5.43 0.353	5.47 0.67		6.0226 0.9655	5.486	0.537	0.06
	5			5.786 1.077	5.64 0.194	5.61 0.201		5.78 0.15	6.2419 0.0489	6.102	0.14	0.49
	6			5.883 0.196	5.88 0.187	5.91 0.165	5.84 0.02		6.4344 0.1934	6.218	0.217	0.31
	7			6.146 0.513	5.78 1.034	6.04 1.272	5.94 1.15		6.5980 0.2540	6.659	0.061	0.62
	8			6.229 0.149	6.17 0.691	6.33 0.764	6.15 0.57		6.8529 0.1008	6.981	0.128	0.65
	9				6.95 0.002	7.11 0.003	6.72 0.15		7.2399 0.0378
	10								7.5841 0.0006
	11								7.7013 0.0035
	12								7.8613 0.0464	7.795	0.066
	13								7.9459 0.0085
	14								7.9979 0.0016

Table 7 .

 7 Quinoline: Rydberg Series

	Rydberg series label	ion state limit	n members	quantum defect δ	Rydberg transition
	R1	D 0 8.628 eV n = 3-16	δ ≈ 1.0	1 1 A′ → (HOMO)π -1 ns
	R2	D 0 8.628 eV n = 3-7	δ ≈ 0.67	1 1 A′ → (HOMO)π -1 np 1
	R3	D 3 10.623 eV	n = 3-9	δ ≈ 0.98	1 1 A′ → (HOMO-3)π -1 ns
	R4	D 3 10.623 eV	n = 3-6	δ ≈ 0.66	1 1 A′ → (HOMO-3)π -1 np 1
	R5	D 3 10.623 eV	n = 3-8	δ ≈ 0.28	1 1 A′ → (HOMO-3)π -1 np 2
	R6	D 4 11.355 eV	n = 3-5	δ ≈ 0.98	1 1 A′ → (HOMO-4)π -1 ns
	R7	D 4 11.355 eV	n = 3-5	δ ≈ 0.72	1 1 A′ → (HOMO-4)π -1 np 1
	R8	D 4 11.355 eV	n = 3-(5)	δ ≈ 0.25	1 1 A′ → (HOMO-4)π -1 np 2

■ ACKNOWLEDGMENTS

We thank N. Champion for technical assistance in the initial study of quinoline.