Peer-reviewed Publications |
Asselin, P., Soulard, P., Madebène, B., Goubet, M., Huet, T. R., Georges, R., Pirali, O., & & Roy, P. (2014). The cyclic ground state structure of the HF trimer revealed by far infrared jet-cooled Fourier transform spectroscopy. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 16, 4797–4806.
Résumé: The rovibrationally resolved Fourier transform (FT) far infrared (FIR) spectra of two intermolecular librations of (HF)3, namely the in-plane n6 and out-of-plane n4 bending fundamentals centered, respectively, at about 494 cm1 and 602 cm1, have been recorded for the first time under jet-cooled conditions using the supersonic jet of the Jet-AILES apparatus. The simultaneous rotational analysis of 245 infrared transitions belonging to both bands enabled us to determine the ground state (GS), n6 and n4 rotational and centrifugal distortion constants. These results provided definite experimental answers to the structure of such a weakly
bound trimer: firstly the vibrationally averaged planarity of cyclic (HF)3, also supported by the very small value of the inertia defect obtained in the GS, secondly the slight weakening of the hydrogen bond in the intermolecular excited states evidenced from the center of mass separations of the HF constituents
determined in the ground, n6 = 1 and n4 = 1 states of (HF)3 as well as the decrease of the fitted rotational constants upon excitation. Finally, lower bounds of about 2 ns on n6 and n4 state lifetimes could be derived from the deconvolution of experimental linewidths. Such long lifetimes highlight the interest in probing low frequency intermolecular motions of molecular complexes to get rid of constraints related to the vibrational dynamics of coupled anharmonic vibrations at higher energy, resulting in loss of rotational information.
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Boulet, C., Ma, Q., & and Thibault, F. (2014). Line interference using a refined Robert-Bonamy formalism: the test case of the isotropic Raman spectra of autoperturbed N2. JOURNAL OF CHEMICAL PHYSICS, 140(8), 084310.
Résumé: A symmetrized version of the recently developed refined Robert-Bonamy formalism [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys.139, 034305 (2013)] is proposed. This model takes into account line coupling effects and hence allows the calculation of the off-diagonal elements of the relaxation matrix, without neglecting the rotational structure of the perturbing molecule. The formalism is applied to the isotropic Raman spectra of autoperturbed N2 for which a benchmark quantum relaxation matrix has recently been proposed. The consequences of the classical path approximation are carefully analyzed. Methods correcting for effects of inelasticity are considered. While in the right direction, these corrections appear to be too crude to provide off diagonal elements which would yield, via the sum rule, diagonal elements in good agreement with the quantum results. In order to overcome this difficulty, a re-normalization procedure is applied, which ensures that the off-diagonal elements do lead to the exact quantum diagonal elements. The agreement between the (re-normalized) semi-classical and quantum relaxation matrices is excellent, at least for the Raman spectra of N2, opening the way to the analysis of more complex molecular systems.
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Boye-Peronne, S., Gauyacq, D., & Lievin, J. (2014). Theoretical description of electronically excited vinylidene up to 10 eV: First high level ab initio study of singlet valence and Rydberg states. JOURNAL OF CHEMICAL PHYSICS, 141(17), 174317.
Résumé: The first quantitative description of the Rydberg and valence singlet electronic states of vinylidene lying in the 0-10 eV region is performed by using large scale ab initio calculations. A deep analysis of Rydberg-valence interactions has been achieved thanks to the comprehensive information contained in the accurate Multi-Reference Configuration Interaction wavefunctions and an original population analysis highlighting the respective role played by orbital and state mixing in such interactions. The present theoretical approach is thus adequate for dealing with larger than diatomic Rydberg systems. The nine lowest singlet valence states have been optimized. Among them, some are involved in strong Rydberg-valence interactions in the region of the Rydberg state equilibrium geometry. The Rydberg states of vinylidene present a great similarity with the acetylene isomer, concerning their quantum defects and Rydberg molecular orbital character. As in acetylene, strong s-d mixing is revealed in the n = 3 s-d supercomplex. Nevertheless, unlike in acetylene, the close-energy of the two vinylidene ionic cores (2)A1 and (2)B1 results into two overlapped Rydberg series. These Rydberg series exhibit local perturbations when an accidental degeneracy occurs between them and results in avoided crossings. In addition, some Deltal = 1 (s-p and p-d) mixings arise for some Rydberg states and are rationalized in term of electrostatic interaction from the electric dipole moment of the ionic core. The strongest dipole moment of the (2)B1 cationic state also stabilizes the lowest members of the n = 3 Rydberg series converging to this excited state, as compared to the adjacent series converging toward the (2)A1 ionic ground state. The overall energies of vinylidene Rydberg states lie above their acetylene counterpart. Finally, predictions for optical transitions in singlet vinylidene are suggested for further experimental spectroscopic characterization of vinylidene.
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Brechignac, P., Garcia, G. A., Falvo, C., Joblin, C., Kokkin, D., Bonnamy, A., Parneix, P., Pino, T., Pirali, O., Mulas, G., & Nahon, L. (2014). Photoionization of cold gas phase coronene and its clusters: Autoionization resonances in monomer, dimer, and trimer and electronic structure of monomer cation. JOURNAL OF CHEMICAL PHYSICS, 141(16), 164325.
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Calvo, F., Falvo, C., & Parneix, P. (2014). Atomistic Modeling of Vibrational Action Spectra in Polyatomic Molecules: Nuclear Quantum Effects. JOURNAL OF PHYSICAL CHEMISTRY A, 118(29), 5427–5436.
Résumé: The response of a polyatonaic molecule to an infrared (IR) laser pulse of varying frequency has been simulated by classical molecular dynamics simulations and by quantum methods based on the path-integral framework (PIMD), as well as quantum thermal baths (QTBs). The outcome of the trajectories was subsequently processed to predict a dissociation spectrum, from the precalculated rate constant. Naphthalene described by a tight-binding potential energy surface was chosen as a testing ground for the present problem, possibly emitting an hydrogen atom after a 12 ps long pulse. At low field intensities, the heating efficiency of the pulse is found to vary similarly as the IR absorption spectrum for all methods considered, reflecting the validity of linear response in this regime. At fields that are sufficiently high to induce statistical dissociation over mass spectrometry timescales, marked differences appear with the spectral features exhibiting additional broadenings and redshift, especially for quantum mechanical descriptions of nuclear motion. Those excessive broadenings are mostly caused by anharmonicities but also convey the inherent approximations of the semidassical QTB method and point at limitations of the PIMD simulations when used in such strong out-of-equilibrium conditions.
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Coudert, L. H., Martin-Drumel, M. - A., & Pirali, O. (2014). Analysis of the high-resolution water spectrum up to the Second Triad and to J=30. JOURNAL OF MOLECULAR SPECTROSCOPY, 303, 36–41.
Résumé: We report high temperature spectroscopic measurements of water vapor carried out in the far infrared domain. The new data set contains numerous transitions characterized by a J-value larger than 30 and allows us to reach rotational levels of water for which information was either unavailable or inaccurate. This new data set, along with previously published microwave, far infrared, and infrared measurements, is fitted using a modified version of the Bending Rotation approach and allows us to perform the first analysis of the high-resolution spectrum of water vapor up to J = 30 for the ground and (010) states, up to J = 27 for the First Triad States, and up to J = 19 for the Second Triad States. The results of the analysis are used to build a spectroscopic database supporting high-resolution investigations performed at temperatures as high as 1500 K.
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Cuisset, A., Gruet, S., Pirali, O., Chamaille, T., & Mouret, G. (2014). Synchrotron FT-FIR spectroscopy of nitro-derivatives vapors: New spectroscopic signatures of explosive taggants and degradation products. SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 132, 838–845.
Résumé: We report on the first successful rovibrational study of gas phase mononitrotoluene and dinitrotoluene in the TeraHertz/Far-Infrared (THz/FIR) spectral domain. Using the AILES beamline of the synchrotron SOLEIL and a Fourier Transform spectrometer connected to multipass cells, the low-energy vibrational cross-sections of the different isomers of mononitrotoluene have been measured and compared to calculated spectra with the density functional theory including the anharmonic contribution. The active FIR modes of 2,4 and 2,6 dinitrotoluene have been assigned to the vibrational bands measured by Fourier Transform FIR spectroscopy of the gas-phase molecular cloud produced in an evaporating/recondensating system. This study highlights the selectivity of gas phase THz/FIR spectroscopy allowing an unambiguous recognition and discrimination of nitro-aromatic compounds used as explosive taggants.
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Dartois, E., Engrand, C., Brunetto, R., Duprat, J., Pino, T., Quirico, E., Remusat, L., Bardin, N., Briani, G., Mostefaoui, S., Morinaud, G., Crane, B., Szwec, N., Delauche, L., Jamme, F., Sand, C., & Dumas, P. (2014). Interstellar and interplanetary carbonaceous solids in the laboratory. Geochemical Journal, 48(6), 511–518.
Résumé: The interstellar medium (ISM) is a physico-chemical laboratory where extreme conditions are encountered and where particular environmental parameters (e.g., density, reactant nature, radiation, temperature, time scales) define the composition of matter. With present observational possibilities, the fundamental question regarding the possible link between ISM and solar system samples can be addressed by astrophysicists, planetologists, and cosmochemists. This article focuses on observations of diffuse ISM and dust components of molecular clouds, setting constraints on the composition of organic solids and large molecules associated with matter cycling in the Galaxy. This study aims at drawing some commonalities and differences between the materials found in the Solar System and those found in interstellar dust.
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Feraud, G., Pino, T., Falvo, C., Parneix, P., Combriat, T., & Brechignac, P. (2014). Intramolecular Processes Revealed Using UV-Laser-Induced IR-Fluorescence: A New Perspective on the “Channel Three” of Benzene. JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 5(7), 1083–1090.
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Goubet, M., & Pirali, O. (2014). The far-infrared spectrum of azulene and isoquinoline and supporting anharmonic density functional theory calculations to high resolution spectroscopy of polycyclic aromatic hydrocarbons and derivatives. JOURNAL OF CHEMICAL PHYSICS, 140, 044322.
Résumé: In the laboratory, the acquisition and analysis of the rotationally resolved spectra of large molecular systems remain challenging. We report in this paper the rotational analysis of the ν30-GS band of azulene and the ν41-GS band of isoquinoline recorded with synchrotron-based Fourier transform absorption spectroscopy in the far-IR. As a support to rotational analyses, we employed a method based on standard density functional theory calculations performed at the anharmonic level which accurately reproduced the rotational constants of 28 vibrational states of 16 Polycyclic Aromatic Hydrocarbons (PAHs) and aza-derivatives. This method appears as an invaluable support for the spectral assignment of the very congested rotational structures of the infrared bands of PAH species and should be very helpful in the active search of these molecules in space through their pure rotational or rovibrational spectra.
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Gruet, S., Goubet, M., & Pirali, O. (2014). High resolution measurements supported by electronic structure calculations of two naphthalene derivatives: [1,5]- and [1,6]-naphthyridine-Estimation of the zero point inertial defect for planar polycyclic aromatic compounds. JOURNAL OF CHEMICAL PHYSICS, 140(23), 234308.
Résumé: Polycyclic aromatic hydrocarbons (PAHs) molecules are suspected to be present in the interstellar medium and to participate to the broad and unresolved emissions features, the so-called unidentified infrared bands. In the laboratory, very few studies report the rotationally resolved structure of such important class of molecules. In the present work, both experimental and theoretical approaches provide the first accurate determination of the rotational energy levels of two diazanaphthalene: [1,5]- and [1,6]-naphthyridine. [1,6]-naphthyridine has been studied at high resolution, in the microwave (MW) region using a Fourier transform microwave spectrometer and in the far-infrared (FIR) region using synchrotron-based Fourier transform spectroscopy. The very accurate set of ground state (GS) constants deduced from the analysis of the MW spectrum allowed the analysis of the most intense modes in the FIR (nu(38)-GS centered at about 483 cm(-1) and nu(34)-GS centered at about 842 cm(-1)). In contrast with [1,6]-naphthyridine, pure rotation spectroscopy of [1,5]-naphthyridine cannot be performed for symmetry reasons so the combined study of the two intense FIR modes (nu(22)-GS centered at about 166 cm(-1) and nu(18)-GS centered at about 818 cm(-1)) provided the GS and the excited states constants. Although the analysis of the very dense rotational patterns for such large molecules remains very challenging, relatively accurate anharmonic density functional theory calculations appeared as a highly relevant supporting tool to the analysis for both molecules. In addition, the good agreement between the experimental and calculated infrared spectrum shows that the present theoretical approach should provide useful data for the astrophysical models. Moreover, inertial defects calculated in the GS (Delta(GS)) of both molecules exhibit slightly negative values as previously observed for planar species of this molecular family. We adjusted the semi-empirical relations to estimate the zero-point inertial defect (Delta(0)) of polycyclic aromatic molecules and confirmed the contribution of low frequency out-of-plane vibrational modes to the GS inertial defects of PAHs, which is indeed a key parameter to validate the analysis of such large molecules.
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Hartmann, J. M., Boulet, C., Vander Auwera J., El Hamzaoui, H., Capoen, B., & and Bouazaoui, M. (2014). Line broadening of confined CO gas. From molecule-wall to molecule-molecule collisions with pressure. JOURNAL OF CHEMICAL PHYSICS, 140(6), 064302.
Résumé: The infrared absorption in the fundamental band of CO gas confined in porous silica xerogel has been recorded at room temperature for pressures between about 5 and 920 hPa using a high resolution Fourier transform spectrometer. The widths of individual lines are determined from fits of measured spectra and compared with ab initio predictions obtained from requantized classical molecular dynamics simulations. Good agreement is obtained from the low pressure regime where the line shapes are governed by molecule-wall collisions to high pressures where the influence of molecule-molecule interactions dominates. These results, together with those obtained with a simple analytical model, indicate that both mechanisms contribute in a practically additive way to the observed linewidths. They also confirm that a single collision of a molecule with a wall changes its rotational state. These results are of interest for the determination of some characteristics of the opened porosity of porous materials through optical soundings.
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Henchy, C., McCaffrey, J. G., Arabei, S., Pavich, T., Galaup, J. - P., Shafizadeh, N., & Crepin, C. (2014). Free base tetraazaporphine isolated in inert gas hosts: Matrix influence on its spectroscopic and photochemical properties. JOURNAL OF CHEMICAL PHYSICS, 141(12), 124303.
Résumé: The absorption, fluorescence, and excitation spectra of free base tetraazaporphine (H(2)TAP) trapped in Ne, N-2, and Ar matrices have been recorded at cryogenic temperatures. Normal Raman spectra of H(2)TAP were recorded in KBr discs and predicted with density functional theory (DFT) using large basis sets calculations. The vibrational frequencies observed in the Raman Spectrum exhibit reasonable agreement with those deduced from the emission spectra, as well as with frequencies predicted from large basis set DFT computations. The upper state vibrational frequencies, obtained from highly resolved, site selected excitation spectra, are consistently lower than the ground state frequencies. This contrasts with the situation in free base phthalocyanine, where the upper state shows little changes in vibrational frequencies and geometry when compared with the ground state. Investigations of the photochemical properties of H(2)TAP isolated in the three matrices have been performed using the method of persistent spectral hole-burning (PSHB). This technique has been used to reveal sites corresponding to distinct N-H tautomers which were not evident in the absorption spectra. An analysis of the holes and antiholes produced with PSHB in the Q(x) (0-0) absorption band made it possible to identify inter-conversion of distinct host sites.
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Ideguchi, T., Poisson, A., Guelachvili, G., Picque, N., & Hansch, T. W. (2014). Adaptive real-time dual-comb spectroscopy. Nature Communications, 5, 3375.
Résumé: The spectrum of a laser frequency comb consists of several hundred thousand equally spaced lines over a broad spectral bandwidth. Such frequency combs have revolutionized optical frequency metrology and they now hold much promise for significant advances in a growing number of applications including molecular spectroscopy. Despite an intriguing potential for the measurement of molecular spectra spanning tens of nanometres within tens of microseconds at Doppler-limited resolution, the development of dual-comb spectroscopy is hindered by the demanding stability requirements of the laser combs. Here we overcome this difficulty and experimentally demonstrate a concept of real-time dual-comb spectroscopy, which compensates for laser instabilities by electronic signal processing. It only uses free-running mode-locked lasers without any phase-lock electronics. We record spectra spanning the full bandwidth of near-infrared fibre lasers with Doppler-limited line profiles highly suitable for measurements of concentrations or line intensities. Our new technique of adaptive dual-comb spectroscopy offers a powerful transdisciplinary instrument for analytical sciences.
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Ivanov, S. V., Boulet, C., Buzykin, O. G., & and Thibault, F. (2014). Line mixing effects in isotropic Raman spectra of pure N2 : a classical trajectory study. JOURNAL OF CHEMICAL PHYSICS, 141(18), 184306.
Résumé: Line mixing effects in the Q branch of pure N2 isotropic Raman scattering are studied at room temperature using a classical trajectory method. It is the first study using an extended modified version of Gordon's classical theory of impact broadening and shift of rovibrational lines. The whole relaxation matrix is calculated using an exact 3D classical trajectory method for binary collisions of rigid N2 molecules employing the most up-to-date intermolecular potential energy surface (PES). A simple symmetrizing procedure is employed to improve off-diagonal cross-sections to make them obeying exactly the principle of detailed balance. The adequacy of the results is confirmed by the sum rule. The comparison is made with available experimental data as well as with benchmark fully quantum close coupling [F. Thibault, C. Boulet, and Q. Ma, J. Chem. Phys. 140, 044303 (2014)] and refined semi-classical Robert-Bonamy [C. Boulet, Q. Ma, and F. Thibault, J. Chem. Phys. 140, 084310 (2014)] results. All calculations (classical, quantum, and semi-classical) were made using the same PES. The agreement between classical and quantum relaxation matrices is excellent, opening the way to the analysis of more complex molecular systems.
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Jacovella, U., Holland, D. M. P., Boyé-Péronne, S., Joyeux, D., Archer, L. E., de Oliveira, N., Nahon, L., Lucchese, R. R., Xu, H., & Pratt, S. T. (2014). High-resolution photoabsorption spectrum of jet-cooled propyne. JOURNAL OF CHEMICAL PHYSICS, 141(11), 114303.
Résumé: The absolute photoabsorption cross section of propyne was recorded between 62 000 and 88 000 cm(-1) by using the vacuum-ultraviolet, Fourier-transform spectrometer at the Synchrotron Soleil. This cross section spans the region including the lowest Rydberg bands and extends above the Franck-Condon envelope for ionization to the ground electronic state of the propyne cation, (X) over tilde (+). Room-temperature spectra were recorded in a flowing cell at 0.9 cm(-1) resolution, and jet-cooled spectra were recorded at 1.8 cm(-1) resolution and a rotational temperature of similar to 100 K. The reduced widths of the rotational band envelopes in the latter spectra reveal new structure and simplify a number of assignments. Although nf Rydberg series have not been assigned previously in the photoabsorption spectrum of propyne, arguments are presented for their potential importance, and the assignment of one nf series is proposed. As expected from previous photoelectron spectra, Rydberg series are also observed above the adiabatic ionization threshold that converge to the v(3)(+) = 1 and 2 levels of the C C stretching vibration.
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Ma, Q., Boulet, C., & and Tipping, R. H. (2014). Effects on calculated half-widths and shifts from the line coupling for asymmetric-top molecules. JOURNAL OF CHEMICAL PHYSICS, 140(24), 244301.
Résumé: The refinement of the Robert-Bonamy formalism by considering the line coupling for linear molecules developed in our previous studies [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys. 139, 034305 (2013); 140, 104304 (2014)] have been extended to asymmetric-top molecules. For H2O immersed in N2 bath, the line coupling selection rules applicable for the pure rotational band to determine whether two specified lines are coupled or not are established. Meanwhile, because the coupling strengths are determined by relative importance of off-diagonal matrix elements versus diagonal elements of the operator −iS1 − S2, quantitative tools are developed with which one is able to remove weakly coupled lines from consideration. By applying these tools, we have found that within reasonable tolerances, most of the H2O lines in the pure rotational band are not coupled. This reflects the fact that differences of energy levels of the H2O states are pretty large. But, there are several dozen strongly coupled lines and they can be categorized into different groups such that the line couplings occur only within the same groups. In practice, to identify those strongly coupled lines and to confine them into sub-linespaces are crucial steps in considering the line coupling. We have calculated half-widths and shifts for some groups, including the line coupling. Based on these calculations, one can conclude that for most of the H2O lines, it is unnecessary to consider the line coupling. However, for several dozens of lines, effects on the calculated half-widths from the line coupling are small, but remain noticeable and reductions of calculated half-widths due to including the line coupling could reach to 5%. Meanwhile, effects on the calculated shifts are very significant and variations of calculated shifts could be as large as 25%.
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Ma, Q., Boulet, C., & and Tipping, R. H. (2014). Two dimensional symmetric correlation functions of the S operator and two dimensional Fourier transforms: considering the line coupling for P and R lines of linear molecules. JOURNAL OF CHEMICAL PHYSICS, 140(10), 104304.
Résumé: The refinement of the Robert-Bonamy (RB) formalism by considering the line coupling for isotropic Raman Q lines of linear molecules developed in our previous study [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys.139, 034305 (2013)] has been extended to infrared P and R lines. In these calculations, the main task is to derive diagonal and off-diagonal matrix elements of the Liouville operator iS1 − S2 introduced in the formalism. When one considers the line coupling for isotropic Raman Q lines where their initial and final rotational quantum numbers are identical, the derivations of off-diagonal elements do not require extra correlation functions of the Sˆ operator and their Fourier transforms except for those used in deriving diagonal elements. In contrast, the derivations for infrared P and R lines become more difficult because they require a lot of new correlation functions and their Fourier transforms. By introducing two dimensional correlation functions labeled by two tensor ranks and making variable changes to become even functions, the derivations only require the latters’ two dimensional Fourier transforms evaluated at two modulation frequencies characterizing the averaged energy gap and the frequency detuning between the two coupled transitions. With the coordinate representation, it is easy to accurately derive these two dimensional correlation functions. Meanwhile, by using the sampling theory one is able to effectively evaluate their two dimensional Fourier transforms. Thus, the obstacles in considering the line coupling for P and R lines have been overcome. Numerical calculations have been carried out for the half-widths of both the isotropic Raman Q lines and the infrared P and R lines of C2H2 broadened by N2. In comparison with values derived from the RB formalism, new calculated values are significantly reduced and become closer to measurements.
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Majumder, M., Sathyamurthy, N., Vazquez, G. J., & Lefebvre-Brion, H. (2014). Interpretation of the accidental predissociation of the E(1) Pi state of CO. J Chem Phys, 140(16), 164303.
Résumé: A special case of predissociation, known as indirect or accidental predissociation observed in the Rydberg E(1)Pi bound state of CO is discussed. We resort to ab initio potentials in order to determine the plausible mechanism for this predissociation. Values of the predissociation width for the valence k(3)Pi state of CO, as obtained from Fermi's golden rule, are also reported. The predissociation width obtained for the mixed E(1)Pi (v = 1, J = 7) state is 0.033 cm(-1) compared to the experimental value of 0.034 cm(-1). The mixed E – E(') state with J = 28, v = 0 is found to be in near resonance condition with the k(3)Pi (v = 4, J = 28) state, thus providing the means to indirect predissociation.
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Martin-Drumel, M. A., Pirali, O., Falvo, C., Parneix, P., Gamboa, A., Calvo, F., & Brechignac, P. (2014). Low-energy vibrational spectra of flexible diphenyl molecules: biphenyl, diphenylmethane, bibenzyl and 2-, 3-and 4-phenyltoluene. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 16(40), 22062–22072.
Résumé: Gas phase absorption far-infrared (FIR) spectra of six flexible hydrocarbon molecules containing two phenyl groups biphenyl, diphenylmethane, bibenzyl and 2-, 3-, 4-phenyltoluene- are reported for the first time, allowing an accurate determination of most of their active low-frequency vibrational modes. DFT calculations have been carried out at the harmonic and perturbative anharmonic levels to predict the vibrational spectra of these molecules and unambiguously assign observed vibrational modes.
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Martin-Drumel, M. A., Pirali, O., & Vervloet, M. (2014). Synchrotron Based FT-FIR Pure Rotational Spectroscopy of the NH2 Radical in Its Two Lowest Vibrational States. JOURNAL OF PHYSICAL CHEMISTRY A, 118(8), 1331–1338.
Résumé: Six Fourier-transform FIR spectra of the NH2 radical have been recorded at high resolution (0.001 cm(-1)) using synchrotron radiation on the AILES beamline at SOLEIL Synchrotron. Three different experimental discharge setups have been used to observe, in absorption, 1009 pure rotational transitions of NH2 in the vibrational ground state (000) and 170 pure rotational transitions within the first excited vibrational state (010). These results constitute a significant extension of the observed quantum numbers for these two states. The spectra permitted several couplings to be resolved (asymmetric coupling, spin-rotation coupling, hyperfine structure) for relatively highly excited energy levels. An effective fit has been realized using both standard Watson-S and -A reductions despite an abnormal centrifugal distortion effect for this light hydride.
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Meek, S., Poisson, A., Guelachvili, G., Hansch, T. W., & Picque, N. (2014). Fourier transform spectroscopy around 3 μm with a broad difference frequency comb. Applied Physics B-Lasers And Optics, 114(4), 573–578.
Résumé: We characterize a new mid-infrared frequency comb generator based on difference frequency generation around 3.1 μm. High power per comb mode (> 10(-7) W/mode) is obtained over a broad spectral span (> 750 nm, > 790 cm(-1)). The source is used for direct absorption spectroscopy with a Michelson-based Fourier transform interferometer.
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Pirali, O., Boudon, V., Carrasco, N., & Dartois, E. (2014). Rotationally resolved IR spectroscopy of hexamethylenetetramine (HMT) C6N4H12. ASTRONOMY & ASTROPHYSICS, 561, A109.
Résumé: Context. Hexamethylenetetramine (HMT) appears to be a potential constituent of several objects in space, including comets or Titan's atmosphere and, as an organic residue of ice irradiation in the laboratory, it may be present in the interstellar medium.
Aims. We performed a laboratory study of rotationally resolved intense IR bands of HMT to provide accurate line positions and synthetic spectra to be used for potential astronomical detections.
Methods. We used synchrotron-based high-resolution Fourier transform infrared spectroscopy to record the experimental data. A formalism and programs dedicated to the assignment, analysis, and simulation of absorption spectra of tetrahedral molecules were used to exploit the spectra.
Results. Infrared spectra of gas phase HMT were recorded and accurate wavenumbers and molecular parameters for four intense bands located in the 1000-1500 cm(-1) spectral range suitable for astronomical searches were derived.
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Quirico, E., Orthous-Daunay, F. - R., Beck, P., Bonal, L., Brunetto, R., Dartois, E., Pino, T., Montagnac, G., Rouzaud, J. - N., Engrand, C., & Duprat, J. (2014). Origin of insoluble organic matter in type 1 and 2 chondrites: New clues, new questions. GEOCHIMICA ET COSMOCHIMICA ACTA, 136, 80–99.
Résumé: Insoluble organic matter (IOM) extracted from primitive chondrites is a polyaromatic solid with a structure and composition resembling that of terrestrial kerogens. A survey of its composition and structure has been carried out on a series of 27 CR, CM, CI and ungrouped C2 carbonaceous chondrites (Tagish Lake, Bells, Essebi, Acfer 094) using infrared and multi-wavelength Raman micro-spectroscopy (244, 514 and 785 nm laser excitations). The results show that chondritic IOM from PCA 91008 (CM2), WIS 91600 (CM2), QUE 93005 (CM2), Tagish Lake (C2 ungrouped) and possibly Cold Bokkeveld (CM2) has been subjected to the past action of short duration thermal metamorphism, presumably triggered by impacts. The IOM in most of the CM chondrites that experienced moderate to heavy aqueous alteration may have been slightly modified by collision-induced heating. However, even IOM from chondrites that escaped significant thermal metamorphism displays Raman characteristics consistent with a formation by thermal processing, either in the protosolar disk or in the parent body. An alternative energetic process to thermal heating is ion irradiation. After thoroughly analyzing both these scenarii, no conclusion can be drawn as to which is the most plausible mechanism nor whether the heating process took place prior or after accretion. The results show for the first time that the width of the G band in spectra collected with a 514 nm excitation correlates with the O/C atomic ratio, suggesting a major role of oxygen in the cross-linking of polyaromatic units.
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Rousselot, P., Pirali, O., Jehin, E., Vervloet, M., Hutsemekers, D., Manfroid, J., Cordier, D., Martin-Drumel, M. - A., Gruet, S., Arpigny, C., Decock, A., & Mousis, O. (2014). Toward a unique nitrogen isotopic ratio in cometary ices. ASTROPHYSICAL JOURNAL LETTERS, 780(2), L17.
Résumé: Determination of the nitrogen isotopic ratios in different bodies of the solar system provides important information regarding the solar system's origin. We unambiguously identified emission lines in comets due to the (NH2)-N-15 radical produced by the photodissociation of (NH3)-N-15. Analysis of our data has permitted us to measure the N-14/N-15 isotopic ratio in comets for a molecule carrying the amine (-NH) functional group. This ratio, within the error, appears similar to that measured in comets in the HCN molecule and the CN radical, and lower than the protosolar value, suggesting that N-2 and NH3 result from the separation of nitrogen into two distinct reservoirs in the solar nebula. This ratio also appears similar to that measured in Titan's atmospheric N-2, supporting the hypothesis that, if the latter is representative of its primordial value in NH3, these bodies were assembled from building blocks sharing a common formation location.
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Shafizadeh, N., Ha-Thi, M. - H., Poisson, L., Soep, B., & Maillard, P. (2014). Observation in the gas phase of the ligation of 1-Methylimidazole to hemoprotein mimics. JOURNAL OF CHEMICAL PHYSICS, 141(17), 174310.
Résumé: Hemoprotein mimics, cobalt picket fence porphyrins have been prepared in the gas phase as neutral molecules for the first time. Their ligation properties have been studied with 1-methylimidazole and compared with those of other cobalt porphyrins, tetraphenyl porphyrin, and cobalt protoporphyrin IX chloride, in view of studying the sterical properties of the ligation. It is shown that the cobalt picket fence porphyrin can only accept one 1-methylimidazole ligand in contrast to less sterically crowded porphyrins like cobalt tetraphenylporphyrin that present two accessible ligation sites. The femtosecond dynamics of these ligated systems have been studied after excitation at 400 nm, in comparison with the unligated ones. The observed transients are formed in much shorter times, 30 fs for the ligated species, as compared to free species (100 fs), supporting the porphyrin to metal charge transfer nature of these transients. The similar decays of the ligated transients <1 ps reveal the absence of photodissociation of the cobalt-1-methylimidazole bond at this step of evolution.
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Thibault, F., Ma Q., & and Boulet, C. (2014). Line coupling effects in the isotropic Raman spectra of N2: A quantum calculation at room temperature. JOURNAL OF CHEMICAL PHYSICS, 140(4), 044303.
Résumé: We present quantum calculations of the relaxation matrix for the Q branch of N2 at room temperature using a recently proposed N2-N2 rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10 200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures.
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Actes de Conférences |
Ideguchi, T., Holzner, S., Bernhardt, B., Guelachvili, G., Hansch, T. W., & Picque, N. (2014). Coherent Raman dual-comb spectroscopy and imaging. In Real-Time Photonic Measurements (Vol. 9279).
Résumé: The invention of the optical frequency comb technique has revolutionized the field of precision spectroscopy, providing a way to measure the absolute frequency of any optical transition. Since, frequency combs have become common equipment for frequency metrology. In the last decade, novel applications for the optical frequency comb have been demonstrated beyond its original purpose. Broadband molecular spectroscopy is one of those. One such technique of molecular spectroscopy with frequency combs, dual-comb Fourier transform spectroscopy provides short measurement times with resolution and accuracy. Two laser frequency combs with slightly different repetition frequencies generate pairs of pulses with a linearly-scanned delay between pulses in a pair. The system without moving parts mimics a fast scanning Fourier transform interferometer. The measurement speed may be several orders of magnitude faster than that of a Michelson-based Fourier transform spectrometer, which opens up new opportunities for broadband molecular spectroscopy. Recently, dual-comb spectroscopy has been extended to nonlinear phenomena. A broadband Raman spectrum of molecular fingerprints may be measured within a few tens of microseconds with coherent Raman dual-comb spectroscopy. Raster scanning the sample leads to hyperspectral images. This rapid and broadband label-free vibrational spectroscopy and imaging technique might provide new diagnostic methods in a variety of scientific and industrial fields.
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