Peer-reviewed Publications |
Beroff, K., Van-Oanh, N. T., Chabot, M., Tuna, T., Pino, T., Martinet, G., Le Padellec, A., Carpentier, Y., & Lavergne, L. (2011). Fragmentation of multiply charged hydrocarbon molecules CnHq+ (n <= 4, q <= 9) produced in high-velocity collisions: Branching ratios and kinetic energy release of the H+ fragment. PHYSICAL REVIEW A, 84(3), 032705.
Résumé: Fragmentation branching ratios for channels involving H+ emission and associated kinetic energy release of the H+ fragment [KER(H+)] have been measured for multicharged CnHq+ molecules produced in high velocity (3.6 a.u.) collisions between CnH+ projectiles and helium atoms. For CHq+ (q <= 4) molecules, measured KER(H+) were found well below predictions of the simple point charge Coulomb model (PCCM) for all q values. Multireference configuration interaction (MRCI) calculations for ground as well as electronic excited states were performed which allowed a perfect interpretation of the CHq+ experimental results for low charges (q = 2-3) as well as for the highest charge (q = 4). In this last case we could show, on the basis of ionization cross sections calculations and experimental measurements performed on the same systems at slightly higher velocity (4.5 a.u.), the prominent role played by inner-shell ionization followed by Auger relaxation and could extract the lifetime of this Auger relaxation giving rise to the best agreement between the experiment and the calculations. For dissociation of C2Hq+ and C3Hq+ with the highest charges (q >= 5), inner-shell ionization contributed in a prominent way to the ion production. In these two cases it was shown that measured KER(H+) were in good agreement with PCCM predictions when those were corrected for Auger relaxation with the same Auger lifetime value as in CH3+.
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Calvo, F., Basire, M., & Parneix, P. (2011). Temperature Effects on the Rovibrational Spectra of Pyrene-Based PAHs. JOURNAL OF PHYSICAL CHEMISTRY A, 115(32), 8845–8854.
Résumé: Absorption infrared spectra have been computed for a variety of polycyclic aromatic hydrocarbon molecules of the pyrene family, taking into account anharmonicity and temperature effects, rovibrational quantization, and couplings. The energy levels are described by a second-order perturbative expansion of the rovibrational Hamiltonian in the vibrational and rotational quantum numbers, as relevant for a symmetric-top molecule, with ingredients obtained from quantum chemistry calculations. Multicanonical Monte Carlo simulations are carried out to compute bidimensional IR intensity histograms as a function of total energy and vibrational frequency, which then provide the absorption spectrum at arbitrary temperatures via a Laplace transformation. The main spectral features analyzed for neutral, anionic, and cationic pyrene indicate a strong dependence on temperature, in agreement with existing laboratory experiments, and a significant contribution of rotational degrees of freedom to the overall broadenings. The spectral shifts and broadenings reveal some sensitivity of anharmonicities to the charge and protonation states and, in the case of protonated pyrene and pyrenyl cation, on possible isomers and between aromatic and aliphatic C-H bands. Implications of the present work to the general issue of interstellar emission features are discussed.
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Chabot, M., Martinet, G., Beroff, K., Pino, T., Bouneau, S., Genolini, B., Grave, X., Nguyen, K., le Gailliard, C., Rosier, P., Feraud, G., Friha, H., & Villier, B. (2011). Detection of atomic and molecular mega-electron-volt projectiles using an x-ray charged coupled device camera. REVIEW OF SCIENTIFIC INSTRUMENTS, 82(10), 103301.
Résumé: We show that an x-ray charge coupled device (CCD) may be used as a particle detector for atomic and molecular mega-electron-volt (MeV) projectiles of around a few hundred keV per atomic mass unit. For atomic species, spectroscopic properties in kinetic energy measurements (i.e., linearity and energy resolution) are found to be close to those currently obtained with implanted or surface barrier silicon particle detectors. For molecular species, in order to increase the maximum kinetic energy detection limit, we propose to put a thin foil in front of the CCD. This foil breaks up the molecules into atoms and spreads the charges over many CCD pixels and therefore avoiding saturation effects. This opens new perspectives in high velocity molecular dissociation studies with accelerator facilities. (C) 2011 American Institute of Physics. [doi:10.1063/1.3640411]
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Cirtog, M., Asselin, P., Soulard, P., Tremblay, B., Madebne, B., Alikhani, M. E., Georges, R., Moudens, A., Goubet, M., Huet, T. R., Pirali, O., & Roy, P. (2011). The (CH2)2O-H2O Hydrogen Bonded Complex. Ab Initio Calculations and Fourier Transform Infrared Spectroscopy from Neon Matrix and a New Supersonic Jet Experiment Coupled to the Infrared AILES Beamline of Synchrotron SOLEIL. JOURNAL OF PHYSICAL CHEMISTRY A, 115(12), 2523–2532.
Résumé: A series of hydrogen bonded complexes involving oxirane and water molecules have been studied. In this paper we report on the vibrational study of the oxirane−water complex (CH2)2O−H2O. Neon matrix experiments and ab initio anharmonic vibrational calculations have been performed, providing a consistent set of vibrational frequencies and anharmonic coupling constants. The implementation of a new large flow supersonic jet coupled to the Bruker IFS 125 HR spectrometer at the infrared AILES beamline of the French synchrotron SOLEIL (Jet-AILES) enabled us to record first jet-cooled Fourier transform infrared spectra of oxirane−water complexes at different resolutions down to 0.2 cm−1. Rovibrational parameters and a lower bound of the predissociation lifetime of 25 ps for the v(OH)b = 1 state have been derived from the rovibrational analysis of the ν(OH)b band contour recorded at respective rotational temperatures of 12 K (Jet-AILES) and 35 K (LADIR jet).
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Crepin, C., Turowski, M., Ceponkus, J., Douin, S., Boye-Peronne, S., Gronowski, M., & Kolos, R. (2011). UV-induced growth of cyanopolyyne chains in cryogenic solids. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(37), 16780–16785.
Résumé: UV laser excitation of cryogenic solids doped with cyanoethyne, HC(3)N, led to an in situ creation of longer carbon-nitrogen chains, namely HC(5)N, C(4)N(2), and C(6)N(2), heralded by their strong visible luminescence. HC(5)N and C(4)N(2) molecules can form, most probably, within HC(3)N aggregates linked by hydrogen bonds, while the reaction occurring between two isolated, photochemically created C(3)N radicals yields C(6)N(2). This latter species, dicyanobutadiyne, is easily detected in Ar, Kr, N(2), as well as in parahydrogen solids. The C(6)N(2) phosphorescence is identified here for the first time. The reported carbon chain coupling reactions in rigid environments are of interest for astrochemistry of interstellar ices.
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Falvo, C., & Meier, C. (2011). A fluctuating quantum model of the CO vibration in carboxyhemoglobin. JOURNAL OF CHEMICAL PHYSICS, 134(21), 214106.
Résumé: In this paper, we present a theoretical approach to construct a fluctuating quantum model of the CO vibration in heme-CO proteins and its interaction with external laser fields. The methodology consists of mixed quantum-classical calculations for a restricted number of snapshots, which are then used to construct a parametrized quantum model. As an example, we calculate the infrared absorption spectrum of carboxy-hemoglobin, based on a simplified protein model, and found the absorption linewidth in good agreement with the experimental results.
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Gans, B., Boye-Peronne, S., Broquier, M., Delsaut, M., Douin, S., Fellows, C. E., Halvick, P., Loison, J. - C., Lucchese, R. R., & Gauyacq, D. (2011). Photolysis of methane revisited at 121.6 nm and at 118.2 nm: quantum yields of the primary products, measured by mass spectrometry. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(18), 8140–8152.
Résumé: Methane photolysis has been performed at the two Vacuum UltraViolet (VUV) wavelengths, 121.6 nm and 118.2 nm, via a spectrally pure laser pump-probe technique. The first photon is used to dissociate methane (either at 121.6 nm or at 118.2 nm) and the second one is used to ionise the CH(2) and CH(3) fragments. The radical products, CH(3)(X), CH(2)(X), CH(2)(a) and C((1)D), have been selectively probed by mass spectrometry. In order to quantify the fragment quantum yields from the mass spectra, the photoionisation cross sections have been carefully evaluated for the CH(2) and CH(3) radicals, in two steps: first, theoretical ab initio approaches have been used in order to determine the pure electronic photoionisation cross sections of CH(2)(X) and CH(2)(a), and have been rescaled with respect to the measured absolute photoionisation cross section of the CH(3)(X) radical. In a second step, in order to take into account the substantial vibrational energy deposited in the CH(3)(X) and CH(2)(a) radicals, the variation of their cross sections near threshold has been simulated by introducing the pertinent Franck-Condon overlaps between neutral and cation species. By adding the interpolated values of CH quantum yields measured by Rebbert and Ausloos [J. Photochem., 1972, 1, 171-176], a complete set of fragment quantum yields has been derived for the methane photodissociation at 121.6 nm, with carefully evaluated 1 sigma uncertainties: Phi[CH(3)(X)] = 0.42 +/- 0.05, Phi[CH(2)(a)] = 0.48 +/- 0.05, Phi[CH(2)(X)] = 0.03 +/- 0.08, Phi[CH(X)] = 0.07 +/- 0.01. These new data have been measured independently of the H atom fragment quantum yield, subject to many controversies in the literature. From our results, we evaluate Phi(H) = 0.55 +/- 0.17 at 121.6 nm. The quantum yields for the photolysis at 118.2 nm differ notably from those measured at 121.6 nm, with a substantial production of the CH(2)(X) fragment: Phi[CH3(X)] = 0.26 +/- 0.04, Phi[CH(2)(a)] = 0.17 +/- 0.05, Phi[CH(2)(X)] = 0.48 +/- 0.06, Phi[CH(X)] = 0.09 +/- 0.01, Phi(H) = 1.31 +/- 0.13. These new data should bring reliable and essential inputs for the photochemical models of the Titan atmosphere.
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Gans, B., Garcia, G. A., Boye-Peronne, S., Loison, J. C., Douin, S., Gaie-Levrel, F., & Gauyacq, D. (2011). Absolute Photoionization Cross Section of the Ethyl Radical in the Range 8-11.5 eV: Synchrotron and Vacuum Ultraviolet Laser Measurements. JOURNAL OF PHYSICAL CHEMISTRY A, 115(21), 5387–5396.
Résumé: The absolute photoionization cross section of C(2)H(5) has been measured at 10.54 eV using vacuum ultraviolet (VUV) laser photoionization. The C(2)H(5) radical was produced in situ using the rapid C(2)H(6) + F -> C(2)H(5) + HF reaction. Its absolute photoionization cross section has been determined in two different ways: first using the C(2)H(5) + NO(2) -> C(2)H(5)O + NO reaction in a fast flow reactor, and the known absolute photoionization cross section of NO. In a second experiment, it has been measured relative to the known absolute photoionization cross section of CH(3) as a reference by using the CH(4) + F -> CH(3) + HF and C(2)H(6) + F -> C(2)H(5) + HF reactions successively. Both methods gave similar results, the second one being more precise and yielding the value: sigma(ion)(C1HS) = (5.6 +/- 1.4) Mb at 10.54 eV. This value is used to calibrate on an absolute scale the photoionization curve of C(2)H(5) produced in a pyrolytic source from the C(2)H(5)NO(2) precursor, and ionized by the VUV beam of the DESIRS beamline at SOLEIL synchrotron facility. In this latter experiment, a recently developed ion imaging technique is used to discriminate the direct photoionization process from dissociative ionization contributions to the C(2)H(5)(+) signal. The imaging technique applied on the photoelectron signal also allows a slow photoelectron spectrum with a 40 meV resolution to be extracted, indicating that photoionization around the adiabatic ionization threshold involves a complex vibrational overlap between the neutral and cationic ground states, as was previously observed in the literature. Comparison with earlier photoionization studies, in particular with the photoionization yield recorded by Ruscic et al.(1) is also discussed.
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Godard, M., Feraud, G., Chabot, M., Carpentier, Y., Pino, T., Brunetto, R., Duprat, J., Engrand, C., Brechignac, P., d'Hendecourt, L., & Dartois, E. (2011). Ion irradiation of carbonaceous interstellar analogues Effects of cosmic rays on the 3.4 μm interstellar absorption band. ASTRONOMY & ASTROPHYSICS, 529, A146.
Résumé: Context. A 3.4 μm absorption band (around 2900 cm(-1)), assigned to aliphatic C-H stretching modes of hydrogenated amorphous carbons (a-C: H), is widely observed in the diffuse interstellar medium, but disappears or is modified in dense clouds. This spectral difference between different phases of the interstellar medium reflects the processing of dust in different environments. Cosmic ray bombardment is one of the interstellar processes that make carbonaceous dust evolve. Aims. We investigate the effects of cosmic rays on the interstellar 3.4 μm absorption band carriers. Methods. Samples of carbonaceous interstellar analogues (a-C: H and soot) were irradiated at room temperature by swift ions with energy in the MeV range (from 0.2 to 160 MeV). The dehydrogenation and chemical bonding modifications that occurred during irradiation were studied with IR spectroscopy. Results. For all samples and all ions/energies used, we observed a decrease of the aliphatic C-H absorption bands intensity with the ion fluence. This evolution agrees with a model that describes the hydrogen loss as caused by the molecular recombination of two free H atoms created by the breaking of C-H bonds by the impinging ions. The corresponding destruction cross section and asymptotic hydrogen content are obtained for each experiment and their behaviour over a large range of ion stopping powers are inferred. Using elemental abundances and energy distributions of galactic cosmic rays, we investigated the implications of these results in different astrophysical environments. The results are compared to the processing by UV photons and H atoms in different regions of the interstellar medium. Conclusions. The destruction of aliphatic C-H bonds by cosmic rays occurs in characteristic times of a few 10(8) years, and it appears that even at longer time scales, cosmic rays alone cannot explain the observed disappearance of this spectral signature in dense regions. In diffuse interstellar medium, the formation by atomic hydrogen prevails over the destruction by UV photons (destruction by cosmic rays is negligible in these regions). Only the cosmic rays can penetrate into dense clouds and process the corresponding dust. However, they are not efficient enough to completely dehydrogenate the 3.4 μm carriers during the cloud lifetime. This interstellar component should be destroyed in interfaces between diffuse and dense interstellar regions where photons still penetrate but hydrogen is in molecular form.
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Hartmann, J. - M., & Boulet, C. (2011). Molecular dynamics simulations for CO2 spectra. III. Permanent and collision-induced tensors contributions to light absorption and scattering. JOURNAL OF CHEMICAL PHYSICS, 134(18), 184312.
Résumé: Classical molecular dynamics simulations have been performed for gaseous CO2 starting from an accurate anisotropic intermolecular potential. Through calculations of the evolutions of the positions and orientations of a large number of molecules, the time evolutions of the permanent and collision-induced electric dipole vector and polarizability tensor are obtained. These are computed from knowledge of static molecular parameters taking only the leading induction terms into account. The Laplace transforms of the auto-correlation functions of these tensors then directly yield the light absorption and scattering spectra. These predictions are, to our knowledge, the first in which the contributions of permanent and collision-induced tensors are simultaneously taken into account for gaseous CO2, without any adjusted parameter. Comparisons between computations and measurements are made for absorption in the region of the nu(3) infrared band and for depolarized Rayleigh scattering in the roto-translational band. They demonstrate the quality of the model over spectral ranges from the band center to the far wings where the spectrum varies by several orders of magnitude. The contributions of the permanent and interaction-induced (dipole and polarizability) tensors are analyzed for the first time, through the purely permanent (allowed), purely induced, and cross permanent/induced components of the spectra. It is shown that, while the purely induced contribution is negligible when compared to the collision-broadened allowed component, the cross term due to interferences between permanent and induced tensors significantly participates to the wings of the bands. This successfully clarifies the long lasting, confusing situation for the mechanisms governing the wings of the CO2 spectra considered in this work (c) 2011 American Institute of Physics. [doi: 10.1063/1.3589143]
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Hartmann, J. - M., Boulet, C., & Jacquemart, D. (2011). Molecular dynamics simulations for CO2 spectra. II. The far infrared collision-induced absorption band. JOURNAL OF CHEMICAL PHYSICS, 134(9), 094316.
Résumé: Classical molecular dynamics simulations have been carried out for gaseous CO2 starting from various anisotropic intermolecular potential energy surfaces. Through calculations for a large number of molecules treated as rigid rotors, the time evolution of the interaction-induced electric dipole vector is obtained and the Laplace transform of its autocorrelation function gives the collision-induced absorption rototranslational spectrum. The results are successfully compared with those of previous similar calculations before studies of the influences of the intermolecular potential and induced-dipole components are made. The calculated spectra show a significant sensitivity to anisotropic forces consistently with previous analyses limited to the spectral moments. The present results also demonstrate the importance of vibrational and back-induction contributions to the induced dipole. Comparisons between measured far infrared (0-250 cm(-1)) spectra at different temperatures and results calculated without the use of any adjustable parameter are made. When the best and more complete input data are used, the quality of our predictions is similar to that obtained by Gruszka et al. [Mol. Phys. 93, 1007 (1998)] after the introduction of ad hoc short-range overlap contributions. Our results thus largely obviate the need for such contributions the magnitudes of which remain questioned. Nevertheless, problems remain since, whereas good agreements with measurements are obtained above 50 cm(-1), the calculations significantly underestimate the absorption below, a problem which is discussed in terms of various possible error sources. (c) 2011 American Institute of Physics. [doi:10.1063/1.3557681]
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Koubek, J., Boulet, C., Perrin, A., Urban, S., & Hartmann, J. - M. (2011). Line-mixing between rotational Stark components of CH3F self-perturbed and perturbed by helium: Experimental results and IOS analysis. JOURNAL OF MOLECULAR SPECTROSCOPY, 266(1), 12–20.
Résumé: Self- and He-broadening coefficients of microwave transitions of CH3F have been measured with and without the presence of an external electric field. This provides values for the J, K -> J + 1, K (K = 0 – J) transitions for J = 1 and J = 3 as well as for the various J, K, M -> J + 1, K, M' (vertical bar M vertical bar = 0 – K, vertical bar M – M'vertical bar = 0, 1) Stark components. The results and those of a previous experimental study for pure CH3F, which show significant line-mixing effects, are analyzed with a model based on the Infinite Order Sudden approximation. It is shown that the latter leads to very satisfactory modeling of observed values even though no parameter was adjusted since previously and independently determined basic cross-sections are used. The quality of the present predictions is comparable with that obtained previously with a semi-classical approach. Furthermore, it is shown that the previously stated inaccuracy of the IOS model was due to an oversimplified use of this approach. (C) 2011 Elsevier Inc. All rights reserved.
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Martin-Drumel, M. A., Pirali, O., Balcon, D., Brechignac, P., Roy, P., & Vervloet, M. (2011). High resolution far-infrared Fourier transform spectroscopy of radicals at the AILES beamline of SOLEIL synchrotron facility. REVIEW OF SCIENTIFIC INSTRUMENTS, 82(11), 113106.
Résumé: Experimental far-infrared (FIR) spectroscopy of transient species (unstable molecules, free radicals, and ions) has been limited so far in both emission and absorption (mainly by the low probability of spontaneous emission in that spectral range and the low brightness of continuum sources used for absorption measurements, respectively). Nevertheless, the FIR spectral range recently became of high astrophysical relevance thanks to several new observational platforms (HERSCHEL, ALMA...) dedicated to the study of this region suitable for the detection of the emission from cold objects of the interstellar medium. In order to complete the experimental dataset concerning transient species, three discharge experiments dedicated to the recording of high resolution FIR spectra of radicals have been developed at the Advanced Infrared Line Exploited for Spectroscopy (AILES) which extracts the bright FIR synchrotron continuum of the synchrotron facility SOLEIL. These experiments make use of a high resolution (R = 0.001 cm(-1)) Bruker IFS125 Fourier transform (FT) spectrometer. An emission setup (allowing to record spectra of radicals excited at high rotational and vibrational temperatures) and two absorption setups (exploiting the bright synchrotron source at the highest resolution available on the FT) are alternatively connected to the FT. The advantages and limitations of these techniques are discussed on the basis of the recent results obtained on OH and CH radicals. These results constitute the first FIR spectra of radicals using synchrotron radiation, and the first FIR spectrum of a C-bearing radical using FT-spectroscopy.
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Murray, C., Dozova, N., McCaffrey, J. G., Shafizadeh, N., Chin, W., Broquier, M., & Crepin, C. (2011). Visible luminescence spectroscopy of free-base and zinc phthalocyanines isolated in cryogenic matrices. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(39), 17543–17554.
Résumé: The absorption, emission and excitation spectra of ZnPc and H(2)Pc trapped in Ne, N(2), Ar, Kr and Xe matrices have been recorded in the region of the Q states. A comparison of the matrix fluorescence spectra with Raman spectra recorded in KBr pellets reveals very strong similarities. This is entirely consistent with the selection rules and points to the occurrence of only fundamental vibrational transitions in the emission spectra. Based on this behaviour, the vibronic modes in emission have been assigned using results obtained recently on the ground state with large basis-set DFT calculations [Murray et al. PCCP, 12, 10406 (2010)]. Furthermore, the very strong mirror symmetry between excitation and emission has allowed these assignments to be extended to the excitation (absorption) bands. While this approach works well for ZnPc, coupling between the band origin of the S(2)(Q(Y)) state and vibrationally excited levels of S(1)(Q(X)), limits the range of its application in H(2)Pc. The Q(X)/Q(Y) state coupling is analysed from data obtained from site-selective excitation spectra, revealing pronounced matrix and site effects. From this analysis, the splitting of the Q(X) and Q(Y) states has been determined more accurately than in any previous attempts.
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Shafizadeh, N., Ha-Thi, M. H., Soep, B., Gaveau, M. A., Piuzzi, F., & Pothier, C. (2011). Spectral characterization in a supersonic beam of neutral chlorophyll a evaporated from spinach leaves. JOURNAL OF CHEMICAL PHYSICS, 135(11), 114303.
Résumé: The observation of the light absorption of neutral biomolecules has been made possible by a method implemented for their preparation in the gas phase, in supersonically cooled molecular beams, based upon the work of Focsa et al. [C. Mihesan, M. Ziskind, B. Chazallon, E. Therssen, P. Desgroux, S. Gurlui, and C. Focsa, Appl. Surf. Sci. 253, 1090 (2006)]. The biomolecules diluted in frozen water solutions are entrained in the gas plume of evaporated ice generated by an infrared optical parametric oscillators (OPO) laser tuned close to its maximum of absorption, at ~3 mum. The biomolecules are then picked up in the flux of a supersonic expansion of argon. The method was tested with indole dissolved in water. The excitation spectrum of indole was found cold and large clusters of indole with water were observed up to n = 75. Frozen spinach leaves were examined with the same method to observe the chlorophyll pigments. The Q(y) band of chlorophyll a has been observed in a pump probe experiment. The Q(y) bands of chlorophyll a is centred at 647 nm, shifted by 18 nm from its position in toluene solutions. The ionization threshold could also be determined as 6.1 0.05 eV.
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Sironneau, V., Chelin, P., Tchana, F. K., Kleiner, I., Pirali, O., Roy, P., Guillemin, J. - C., Orphal, J., Margules, L., Motiyenko, R. A., Cooke, S. A., Youngblood, W. J., Agnew, A., & Dewberry, C. T. (2011). Reinvestigation of the microwave and new high resolution far-infrared spectra of cis-methyl nitrite, CH3ONO: Rotational study of the two first torsional states. JOURNAL OF MOLECULAR SPECTROSCOPY, 267(1-2), 92–99.
Résumé: The first far-infrared high resolution absorption measurement of the cis-methyl nitrite molecule has been recorded in the range 15-400 cm(-1) using the synchrotron AILES beamline radiation at SOLEIL with a resolution of 0.0011 cm(-1). First assignments for the pure rotational transitions (15-65 cm(-1)) belonging to the ground nu(t) (=nu(15)) = 0 and first nu(t) = 1 excited torsional state are based on measurements from previous studies performed in the 13-40 GHz spectral range, as well as on new millimeter-wave measurements performed at Lille in the spectral range 75-465 GHz. A few measurements and remeasurements in the 1.8-13 GHz were also performed using the chirped FT-MW spectrometer located in North Texas. The pure rotational transitions in the far-infrared and in the microwave spectral range belonging to the two first torsional states have been globally fitted using the RAM (“Rho Axis Method”) dealing with the rotation-torsion Hamiltonian and implemented in the BELGI code. A total of 708 and 713 microwave transitions (6 <= J <= 40, K-a(max) <= 23) belonging to the ground torsional state nu(t) = 0 and 1 have been fitted with root-mean-square (rms) deviations of 37.4 kHz and 32.3 kHz respectively, and 3170 pure rotational transitions in the far-infrared range (12 <= J(max) <= 65, 0 <= K-a(max) <= 48) belonging to nu(t) = 0 and 1 have been fitted with a rms deviation of 0.00017 cm(-1), using 35 parameters. Since in the far-infrared spectral range, the A-E internal rotor splittings have not been observed for the transitions belonging to the torsional ground nu(t) = 0 state of the cis-methyl nitrite species, another fit was performed on those lines, using a Watson type Hamiltonian for comparison. (C) 2011 Elsevier Inc. All rights reserved.
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Soorkia, S., Shafizadeh, N., Lievin, J., Gaveau, M. - A., Pothier, C., Mestdagh, J. - M., Soep, B., & Field, R. W. (2011). Determination of the Ground Electronic State in Transition Metal Halides: ZrF. J. Phys. Chem. A, 115(34), 9620–9632.
Résumé: The spectroscopy of the ZrF radical, produced by a laser ablation molecular beam experimental setup, has been investigated for the first time using a two-color two-photon (1 + 1') REMPI scheme and time-of-flight (TOF) mass spectrometry detection. The region of intense bands 400-470 nm has been studied, based upon the first spectroscopic observations of the isovalent ZrCl radical by Carroll and Daly.(1) The overall spectrum observed is complex. However, simultaneous and individual ion detection of the five naturally occurring isotopologues of ZrF has provided a crucial means of identifying band origins and characterization via the isotopic shift, delta(iso), of the numerous vibronic transitions recorded. Hence, five (0-0) transitions, of which only two were free of overlap with other transitions, have been identified. The most intense (0-0) transition at 23113 cm(-1) presented an unambiguously characteristic RQP rotational structure. From rotational contour simulations of the observed spectra, the nature of the ground electronic state is found to be unambiguously of (2)Delta symmetry, leading to the assignment of this band as (0-0) (2)Delta <- X(2)Delta at 23113 cm(-1). A set of transitions (1-0) (2)Delta <- X(2)Delta at 22105 cm(-1) and (2-0) (2)Phi <- X(2)Delta at 22944 cm(-1) involving the X(2)Delta state has also been identified and analyzed. Furthermore, a second series of transitions with lesser intensity has also been related to the long-lived metastable (4)Sigma(-) state: (3-0) (4)Pi(-1/2) <- (4)Sigma(-) at 21801 cm(-1), (2-0) (4)Pi(-1/2) <- (4)Sigma(-) at 21285 cm(-1) and (2-0) (4)Sigma(-) <- (4)Sigma(-) at 23568 cm(-1). These spectroscopic assignments are supported by MRCI ab initio calculations, performed using the MOLPRO quantum chemistry package, and show that the low-lying excited states of the ZrF radical are the (4)Sigma(-) and (4)Phi states lying at 2383 and 4179 cm(-1) respectively above the ground X (2)Delta state. The difference in the nature of ground state and ordering of the first electronic states with TiF (X (4)Phi)(2-4) and ZrCl,(s) respectively, is examined in terms of the ligand field theory (LFT)(7) applied to diatomic molecules. These results give a precise description of the electronic structure of the low lying electronic states of the ZrF transition metal radical.
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Tran, H., Boulet, C., Stefani, S., Snels, M., & Piccioni, G. (2011). Measurements and modelling of high pressure pure CO2 spectra from 750 to 8500 cm(-1). I-central and wing regions of the allowed vibrational bands. JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, 112(6), 925–936.
Résumé: Precise modelling of infrared absorption by carbon dioxide is of primary importance for radiative transfer calculations in CO2-rich atmospheres like those of Venus and Mars. Despite various measurements and theoretical models dedicated to this subject, accurate data at different temperatures and pressures are still lacking in numerous spectral regions. In this work, using two Fourier Transform Spectrometers, we have measured spectra of pure CO2 in a large spectral region range, from 750 to 8500 cm(-1) at various densities (3-57 amagat) and temperatures (230-473 K). Comparisons between measured dipolar absorption bands and spectra calculated with the widely used Lorentz line shape show very large discrepancies. This result is expected since the Lorentz approach neglects line-coupling effects due to intermolecular collisions which transfer absorption from the wings to the band center. In order to account for this effect, a theoretical approach based on the impact and Energy Corrected Sudden approximations has been developed. Comparisons of this model with numerous laboratory spectra in a wide range of pressure, temperature and spectral domain show satisfactory agreements for band centers and near wing regions where the impact approximation is valid. However, as expected, due to the breakdown of the impact approximation, the model fails when considering far wing regions. In the absence of precise models accounting for line-mixing and finite collision duration (non impact) effects, empirical approximations are proposed in order to model the far wings. (C) 2010 Elsevier Ltd. All rights reserved.
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Actes de Conférences |
Basire, M., Parneix, P., Pino, T., Brechignac, P., & Calvo, F. (2011). MODELING THE ANHARMONIC INFRARED EMISSION SPECTRA OF PAHS: APPLICATION TO THE PYRENE CATION. In PAHS AND THE UNIVERSE: A SYMPOSIUM TO CELEBRATE THE 25TH ANNIVERSARY OF THE PAH HYPOTHESIS (Vol. 46, pp. 95–101).
Résumé: The IR emission cascade from the pyrene cation due to a broad band optical excitation is simulated using kinetic Monte Carlo. Anharmonicities of the ground electronic state potential energy surface are taken into account in the transition energies, the microcanonical densities of states, and the rate of hydrogen loss through various statistical theories. The emission spectral features of the “3.3”, “6.2” and “11.2” μm bands are computed for different blackbody temperatures.
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Boudon, V., Gabard, T., Pirali, O., Roy, P., Brubach, J. B., Manceron, L., Vander Auwera, J., Coustenis, A., & & Lellouch, E. (2011). LE SPECTRE INFRAROUGE LOINTAIN DU METHANE DANS L’ATMOSPHERE DE TITAN. In L’Actualité Chimique, Le rayonnement synchrotron, une lumière pour comprendre la chimie (Vol. 356, 97).
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Haensch, T. W., & Picque, N. (2011). Molecular Spectroscopy with Laser Frequency Combs. In 2011 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO).
Résumé: The millions of precisely controlled laser comb lines produced with a train of ultrashort laser pulses can harnessed for highly-multiplexed molecular spectroscopy. Multi-heterodyne spectroscopy with frequency combs is emerging as a powerful new tool.
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Parneix, P., & Calvo, F. (2011). Theoretical approaches to nucleation in the gas phase. With a glimpse at experiments and dust formation in astrophysics. In CHEMISTRY IN ASTROPHYSICAL MEDIA (Vol. 18).
Résumé: An overview of the physics of homogeneous nucleation is presented, focusing on the main theoretical approaches that are currently available. We review the microscopic assumptions behind classical nucleation theory, as well as several improvements with various degrees of empiricism. The increasing role played by molecular simulations in testing and correcting nucleation theories is discussed. Typical laboratory experiments on homogeneous nucleation are also reviewed, emphasizing how experimental observables can be compared with theoretical predictions. Finally, the more specific challenges of nucleation in astrophysical media are discussed.
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Pino, T., Carpentier, Y., Feraud, G., Friha, H., Kokkin, D. L., Troy, T. P., Chalyavi, N., Brechignac, P., & Schmidt, T. W. (2011). ELECTRONIC SPECTROSCOPY OF PAHS. In PAHS AND THE UNIVERSE: A SYMPOSIUM TO CELEBRATE THE 25TH ANNIVERSARY OF THE PAH HYPOTHESIS (Vol. 46, pp. 355–371).
Résumé: Polycyclic aromatic hydrocarbons are a class of molecules of broad interest that has long been explored by various spectroscopic techniques. The electronic spectroscopy of these species is of particular interest since it provides a framework for the understanding of the electronic structure of large polyatomic molecules. Such studies also allow the systematic investigation of electronic relaxation mechanisms in large molecules. In this review, we focus on the gas-phase experimental work on such systems and present the latest progress. We also underline the challenges that remain to be tackled. A focus on the understanding of the electronic relaxation pathways at work in gas-phase PAT-Is will also be presented, as well as their possible manifestation in space.
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Wang, C. Y., Herr, T., Del'Haye, P., Schliesser, A., Holzwarth, R., Haensch, T. W., Picque, N., & Kippenberg, T. J. (2011). Mid-Infrared Frequency Combs Based on Microresonators. In 2011 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO).
Résumé: We present for the first time mid-infrared frequency comb generation from micro-resonators. Combs spanning over more than 10 THz around the 2.5 μm-wavelength CW-pump are generated in crystalline MgF(2) whispering-gallery mode resonators via four-wave-mixing.
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Chapitres de Livres |
Shafizadeh, N., Ha-Thi, M. - H., Poisson, L., & Soep, B. (2011). Ultrafast Electronic Relaxation of Excited State of Biomimetic Metalloporphyrins in the Gas Phase. In Biomimetics. Assoc. Prof. Dr. Lilyana D. Pramatarova.
Résumé: Available from: http://www.intechopen.com/articles/show/title/ultrafast-electronic-relaxation-of-excited-state-of-biomimetic-metalloporphyrins-in-the-gas-phase.
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