Peer-reviewed Publications |
Alata, I., Jallat, A., Gavilan, L., Chabot, M., Cruz-Diaz, G. A., Munoz Caro, G. M., Béroff, K., & Dartois, E. (2015). Vacuum ultraviolet of hydrogenated amorphous carbons. A&A, 584, A123.
Résumé: Context. Hydrogenated amorphous carbons (a–C:H) are a major component of the carbonaceous solids present in the interstellar medium. The production and existence of these grains is connected in particular with the balance between their photolysis, radiolysis, and hydrogenation. During grain processing, H2 and other small organic molecules, radicals, and fragments are released into the gas phase.
Aims. We perform photolytic experiments on laboratory produced interstellar a–C:H analogues to monitor and quantify the release of species and compare to relevant observations in the interstellar medium.
Methods. Hydrogenated amorphous carbon analogues at low temperature are exposed to ultraviolet (UV) photons, under ultra-high vacuum conditions. The species produced are monitored using mass spectrometry and post irradiation temperature-programmed desorption. Additional experiments are performed using deuterated analogues and the species produced are unambiguously separated from background contributions. We implement the laboratory measured yields for the released species in a time dependent model to investigate the effect of the UV photon irradiation of hydrogenated amorphous carbons in a photon dominated region, and estimate the associated time scale.
Results. The UV photolysis of hydrogenated amorphous carbons leads to the production of H2 molecules and small hydrocarbons. The model shows that the photolytic evolution of a–C:Hs in photon dominated regions, such as the Horsehead Nebula, can raise the abundance of carbonaceous molecules by several orders of magnitude at intermediate visual extinctions, i.e., after the C+ maximum and before the dense cloud conditions prevail where models generally show a minimum abundance for such carbonaceous species. The injection time peak ranges from a thousand to ten thousand years in the models, considering only the destruction of such grains and no re-hydrogenation. This time scale is consistent with the estimated advection front of a photon dominated region, which replenishes it with freshly exposed material.
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Boulet, C., & Ma, Q. and T., R.H. (2015). Line mixing in parallel and perpendicular bands of CO2: A further refined Robert-Bonamy formalism. Journal of Chemical Physics, 143(12), 124313.
Résumé: Starting from the refined Robert-Bonamy formalism [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys. 139, 034305 (2013)], we propose here an extension of line mixing studies to infrared absorptions of linear polyatomic molecules having stretching and bending modes. The present formalism does not neglect the internal degrees of freedom of the perturbing molecules, contrary to the energy corrected sudden (ECS) modelling, and enables one to calculate the whole relaxation matrix starting from the potential energy surface. Meanwhile, similar to the ECS modelling, the present formalism properly accounts for roles played by all the internal angular momenta in the coupling process, including the vibrational angular momentum. The formalism has been applied to the important case of CO2 broadened by N2. Applications to two kinds of vibrational bands (Σ → Σ and Σ → Π) have shown that the present results are in good agreement with both experimental data and results derived from the ECS model.
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Calvo, F., Li, Y., Kiawi, D. M., Bakker, J. M., Parneix, P., & Janssens, E. (2015). Nonlinear effects in infrared action spectroscopy of silicon and vanadium oxide clusters: experiment and kinetic modeling. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17(39), 25956–25967.
Résumé: For structural assignment of gas phase compounds, infrared action spectra are usually compared to computed linear absorption spectra. However, action spectroscopy is highly nonlinear owing to the necessary transfer of the excitation energy and its subsequent redistribution leading to statistical ionization or dissociation. Here, we examine by joint experiment and dedicated modeling how such nonlinear effects affect the spectroscopic features in the case of selected inorganic clusters. Vibrational spectra of neutral silicon clusters are recorded by tunable IR-UV two-color ionization while IR spectra for cationic vanadium oxide clusters are obtained by IR multiphoton absorption followed by dissociation of the bare cluster or of its complex with Xe. Our kinetic modeling accounts for vibrational anharmonicities, for the laser interaction through photon absorption and stimulated emission rates, as well as for the relevant ionization or dissociation rates, all based on input parameters from quantum chemical calculations. Comparison of the measured and calculated spectra indicates an overall agreement as far as trends are concerned, except for the photodissociation of the V3O7+-Xe messenger complex, for which anharmonicities are too large and poorly captured by the perturbative anharmonic model. In all systems studied, nonlinear effects are essentially manifested by variations in the intensities as well as spectral broadenings. Differences in some band positions originate from inaccuracies of the quantum chemical data rather than specific nonlinear effects. The simulations further yield information on the average number of photons absorbed, which is otherwise unaccessible information: several to several tens of photons need to be absorbed to observe a band through dissociation, while three to five photons can be sufficient for detection of a band via IR-UV ionization.
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Chaussard, F., Vieillard, T., Billard, F., Faucher, O., Hartmann, J. - M., Boulet, C., & Lavorel, B. (2015). Dissipation of post-pulse laser-induced alignment of CO2 through collisions with Ar. J. Raman Spectrosc., 46(8), 691–694.
Résumé: In this paper, laser-induced field-free alignment of CO2 in mixtures with Ar is investigated under dissipative conditions (up to 15 bars) at room temperature. The degree of alignment is temporally monitored by a polarization spectroscopy technique, where a weak probe pulse measures the transient birefringence resulting from the alignment. The data are analyzed with a quantum mechanical density matrix formalism using properly J-dependent and M-dependent state-to-state transfer rates, which was previously successfully tested on pure CO2 and CO2–He mixtures. The same consistency is obtained between experiments and calculations, in particular the decay times of both the transient revivals and the permanent component of the alignment are accurately predicted by the model.
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Depauw, A., Kumar, N., Ha-Thi, M. - H., & Leray, I. (2015). Calixarene-Based Fluorescent Sensors for Cesium Cations Containing BODIPY Fluorophore. The Journal of Physical Chemistry A, 119(23), 6065–6073.
Résumé: New fluorescent molecular sensors based on a calix[4]arene biscrown-6 ether as coordination site and BODIPY derivative as signaling unit were synthesized, and their photophysical properties were characterized. The complexation properties of these sensors with potassium and cesium cations were investigated using both steady-state and time-resolved fluorescence methods. The studies show that the sensitivity with cations depends upon the position of substituted coordination site on the BODIPY core. The complexation with cations does not have much effect on the absorption and emission wavelength when the coordination site (calix[4]arene biscrown-6 ether) is introduced at the meso position of the BODIPY core. In contrast, the same calix[4]arene biscrown-6 ether attached via a styryl linker to the α-position of BODIPY core leads to a sensitive sensor for alkali cations thanks to the better conjugation between the coordination site and the BODIPY core. The complexation of cations induces a hypsochromic shift of the absorption and emission maximums due to the diminution of donor character of the oxygen atoms in the coordination site. The stability constants of complexes with potassium and cesium ion were measured.
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Douin, S., Gronowski, M., Lamarre, N., Phung, V. - T., Boyé-Péronne, S., Crépin, C., & and Kołos, R. (2015). Cavity Ring Down Spectroscopy Measurements for High-Overtone Vibrational Bands of HC3N. Journal of Physical Chemistry A, 119(36), 9494–9505.
Résumé: Overtone (5ν1 and 6ν1) and combination (4ν1+ν3 and 4ν1+ν2) vibrational bands of gaseous HC3N, located in the visible range (14 600-15 800 cm-1 and 17 400-18 600 cm-1), were investigated by cavity ring-down absorption spectroscopy. The 5ν1+ν3 and 5ν1+ν2 combinations as well as the 6ν1+ν5-ν5 hot overtone band have also been identified, based on previous overtone assignments. Absolute integrated intensity values and the ensuing oscillator strengths have been measured here for the first time; f –values are typically confined between 4×10-12 and 7×10-11. For the even weaker 5ν1+ν2 combination band, the oscillator strength was estimated as 9×10-13.
The values concerning CH-stretch overtones (nν1) are similar to those found in the literature for HCN and C2H2, the molecules with sp-hybridized carbon atoms. Data presented here may prove useful for studying the photochemistry triggered with visible or near-IR radiation within the atmospheres of certain Solar System bodies, including Titan.
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Falvo, C., Daniault, L., Vieille, T., Kemlin, V., Lambry, J. - C., Meier, C., Vos, M. H., Bonvalet, A., & and Joffre, M. (2015). Ultrafast Dynamics of Carboxy-Hemoglobin: Two-Dimensional Infrared Spectroscopy: Experiments and Simulations. J. Phys. Chem. Lett., 6, 2216–2222.
Résumé: This Letter presents a comparison between experimental and simulated 2D mid-infrared spectra of carboxy-hemoglobin in the spectral region of the carbon monoxide stretching mode. The simulations rely on a fluctuating potential energy surface that includes both the effect of heme and the protein surroundings computed from molecular dynamics simulations. A very good agreement between theory and experiment is obtained with no adjustable parameters. The simulations show that the effect of the distal histidine through the hydrogen bond is strong and is directly responsible for the slow decay of the frequency-frequency correlation function on a 10 ps time scale. This study confirms that fluctuations in carboxy-hemoglobin are more inhomogeneous than those in the more frequently studied carboxy-myoglobin. The comparison between simulations and experiments brings valuable information on the complex relation between protein structure and spectral diffusion.
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Garcia, G. A., Gans, B., Tanga, X., Ward, M., Batut, S., Nahon, L., Fittschen, C., & Loison, J. - C. (2015). Threshold photoelectron spectroscopy of the imidogen radical. Journal of Electron Spectroscopy and Related Phenomena, 203, 25–30.
Résumé: We present the threshold photoelectron spectroscopy of the imidogen radical (NH) recorded in the photon energy region up to 1 eV above its first ionization threshold. The radical was produced by reaction of NH3 and F in a microwave discharge flow-tube and photoionized using vacuum ultraviolet (VUV) synchrotron radiation. A double imaging coincidence spectrometer was used to record mass-selected spectra and avoid contributions from the byproducts present in the reactor and background gas. The energy region includes the ground X+2Π and first electronically excited a+4Σ− states of NH+. Strong adiabatic transitions and weak vibrational progressions up to v+ = 2 are observed for both electronic states. The rotational profile seen in the origin band has been modeled using existing neutral and cationic spectroscopic constants leading to a precise determination of the adiabatic ionization energy at 13.480 ± 0.002 eV.
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Goubet, M., Soulard, P., Pirali, O., Asselin, P., Réal, F., Gruet, S., Huet, T. R., & Roy, P. and G., R. (2015). Standard free energy of the equilibrium between the trans-monomer and the cyclic-dimer of acetic acid in the gas phase from infrared spectroscopy. Physical Chemistry Chemical Physics, 17(11), 7477–7488.
Résumé: Survey jet-cooled spectra of acetic acid have been recorded in the infrared region (200-4000 cm(-1)) over a wide range of expansion conditions. From the variations of the relative intensities of the signals, vibrational transitions have been assigned unambiguously to the trans-monomer and cyclic-dimer. The IR-active fundamental frequencies have been determined at the instrumental accuracy of 0.5 cm(-1). This analysis of the jet-cooled spectra supported by electronic structure calculations permitted us to characterize the trans-monomer/cyclic-dimer equilibrium. From static cell spectra at 298 K, variations of the molar fractions ratio as a function of the total pressure were used to estimate the equilibrium constant and the Gibbs free energy of dimerization at 298 K. The very good agreement with the literature data shows that the present method is able to produce, from a single study, a free energy value as reliable as the one obtained from a large collection of data. In addition, the semi-empirical free energy value was used to estimate the accuracy of electronic structure calculations and in turn the accuracy of the derived useful information such as the dissociation energy of the complex (i.e. the strength of the hydrogen bonds) or the relative energies within the conformational landscape.
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Jacovella, U., Holland, D. M. P., Boyé-Péronne, S., Gans, B., Joyeux, D., Archer, L. E., de Oliveira, N., Nahon, L., Lucchese, R. R., & Xu, H. and P., S. T. (2015). High-resolution vacuum-ultraviolet photoabsorption spectra of 1-butyne and 2-butyne. J. Chem. Phys., 143, 034304.
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+.
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 ∼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 v3 + = 1 and 2 levels of the C≡C stretching vibration.
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Jacovella, U., Gans, B., & Merkt, F. (2015). Internal rotation, spin–orbit coupling, and low-frequency vibrations in the ground state of CH3–CC–CH+3 and CD3–CC–CD+3. Molecular Physics, 113(15-16), 2115–2124.
Résumé: Pulsed-field-ionisation zero-kinetic-energy (PFI-ZEKE) photoelectron spectra of 2-butyne (CH3–CC–CH3) and its fully deuterated isotopomer have been recorded in the region of the origin band of the ionising transition. The spectral congestion originating from the combined effects of the internal rotation of the methyl groups, the spin–orbit coupling, and the Jahn–Teller effect prevented the full resolution of the rotational structure of the photoelectron spectra. A tentative analysis of the rotational branch structure of the photoelectron spectra using rovibronic photoionisation selection rules derived in the permutation–inversion spin double group G36(M2) suggests a splitting of ∼10.5 cm−1 between the two spin–orbit components E3/2 and E1/2 of the 2 E1 ground state and an almost free internal rotation of the methyl groups in the cations. Assignments are proposed for several low-lying vibrational levels of the cations.
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Jacovella, U., Holland, D. M. P., Boyé-Péronne, S., Gans, B., de Oliveira, N., Ito, K., Joyeux, D., Archer, L. E., Lucchese, R. R., Xu, H., & Pratt, S. T. (2015). A Near-Threshold Shape Resonance in the Valence-Shell Photoabsorption of Linear Alkynes. The Journal of Physical Chemistry A, 119(50), 12339–12348.
Résumé: The room-temperature photoabsorption spectra of a number of linear alkynes with internal triple bonds (e.g., 2-butyne, 2-pentyne, and 2- and 3-hexyne) show similar resonances just above the lowest ionization threshold of the neutral molecules. These features result in a substantial enhancement of the photoabsorption cross sections relative to the cross sections of alkynes with terminal triple bonds (e.g., propyne, 1-butyne, 1-pentyne, ...). Based on earlier work on 2-butyne [Xu et al., J. Chem. Phys. 2012, 136, 154303], these features are assigned to excitation from the neutral highest occupied molecular orbital (HOMO) to a shape resonance with g (l = 4) character and approximate π symmetry. This generic behavior results from the similarity of the HOMOs in all internal alkynes, as well as the similarity of the corresponding gπ virtual orbital in the continuum. Theoretical calculations of the absorption spectrum above the ionization threshold for the 2- and 3-alkynes show the presence of a shape resonance when the coupling between the two degenerate or nearly degenerate π channels is included, with a dominant contribution from l = 4. These calculations thus confirm the qualitative arguments for the importance of the l = 4 continuum near threshold for internal alkynes, which should also apply to other linear internal alkynes and alkynyl radicals. The 1-alkynes do not have such high partial waves present in the shape resonance. The lower l partial waves in these systems are consistent with the broader features observed in the corresponding spectra.
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Kisiel, Z., Martin-Drumel, M. - A., & Pirali, O. (2015). Lowest vibrational states of acrylonitrile from microwave and synchrotron radiation spectra. Spectroscopy with Synchrotron Radiation, 315, 83–91.
Résumé: The high resolution Fourier-transform spectrum of acrylonitrile covering the 40–700cm−1 spectral region was recorded at the AILES infrared beamline of the SOLEIL synchrotron. The spectrum allowed assignment of vibration–rotation transitions in four different fundamental bands, five hot bands, one overtone band, as well as of some pure rotational transitions. The new infrared data and previous measurements made with microwave techniques have been combined into a single global fit encompassing over 31000 measured transitions. Precise vibrational term values have been determined for the eight lowest excited vibrational states, including ν11=228.299930(4), ν15=332.678207(4), ν10=560.716701(5), and ν14=681.793862(13)cm−1. The new values are compared with those obtained previously entirely on the basis of rotational perturbations. Several anharmonicity coefficients are determined and compared with abinitio anharmonic force field calculations. The assignment of the ν10 mode is also clarified.
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Labaigt, G., Jorge, A., Illescas, C., Béroff, K., Dubois, A., Pons, B., & Chabot, M. (2015). Electron capture and ionization processes in high-velocity C+ n , C – Ar and He collisions. J. Phys. B, 48, 075201.
Résumé: Single and double electron capture as well as projectile single and multiple
ionization processes in 125 keV/u C+n- He (n=1-5) and C+n-Ar (n=1,2,4) collisions
have been studied experimentally and theoretically. Helium target single and double
ionization cross sections are also reported for C+n- He (n=1,4) collisions in the 100-400 keV/u impact energy domain. These results are compared with predictions from the Independent Atom and Electron (IAE) model developed to describe cluster-atom collisions. The ion/atom-atom probabilities required for the IAE simulations have been determined by Classical Trajectory Monte Carlo (CTMC) and SemiClassical AtomicOrbital Close-Coupling (SCAOCC) calculations for the Ar and He targets, respectively.
For comparison electron capture cross sections were also measured in C – He and Ar
collisions. In general the agreement between experiment and IAE calculations has been found rather good with the exception of double electron capture leading to anionic Cn- species.
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Lamarre, N., Falvo, C., Alcaraz, C., Cunha de Miranda, B., Douin, S., Flütsch, A., Romanzin, C., Guillemin, J. - C., & Boyé-Péronne, S., Gans, B. (2015). Photoionization spectroscopy of CH3C3N in the vacuum-ultraviolet range. Journal of Molecular Spectroscopy, 315, 206–216.
Résumé: Using vacuum-ultraviolet (VUV) synchrotron radiation, threshold and dissociative photoionization of cyanopropyne (CH3C3N) in the gas phase have been studied from 86000 cm-1 up to 180000 cm-1 by recording Threshold-PhotoElectron Spectrum (TPES)
and PhotoIon Yield (PIY). Ionization energies of the four lowest electronic states X+ 2E, A+ 2A1, B+ 2E and C+ of CH3C3N+ are derived from the TPES with a better accuracy than previously reported. The adiabatic ionization potential of CH3C3N is measured as 86872 +/- 20 cm-1. A description of the vibrational structure of these states is proposed leading to the first determination of the vibrational frequencies for most modes. The vibrational assignments of the X+ state are supported by density functional theory calculations. In addition, dissociative photoionization spectra have been recorded for several cationic fragments in the range 12- 15.5 eV (96790-125000 cm-1) and they bring new information on the photophysics of CH3C3N+. Threshold energies for the cationic dissociative channels leading to CH2C3N+, CHC3N+, HC3H+, HCNH+ and CH+3 have been measured for the first time and are compared with quantum chemical calculations.
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Lamarre, N., Gans, B., Alcaraz, C., Cunha de Miranda, B., Guillemin, J. - C., Broquier, M., Liévin, J., & Boyé-Péronne, S. (2015). Vibronic structure of the 2Πu ground electronic state of dicyanoacetylene cation revisited by PFI-ZEKE photoelectron spectroscopy and ab initio calculations. Molecular Physics, 113(24), 3946–3954.
Résumé: The X+ 2Piu ← X 1Sigma+ g transition of dicyanoacetylene has been recorded for the first time using Pulsed-Field-Ionization ZEro-Kinetic Energy (PFI-ZEKE) photoelectron spectroscopy.
The analysis of the photoelectron spectrum allowed an accurate determination of the adiabatic ionization potential of C4N2 (Ei, ad./hc = 95479±2 cm−1) and a description of the vibrational structure of the electronic ground state of the cation which is affected by Renner-Teller effect and spin-orbit interaction. The spin-orbit coupling constant was measured as −52 ± 2 cm−1.
These results are supported by ab initio calculations performed at the Complete Active Space Self Consistent Field and Second order Perturbation Theory (CASSCF and CASPT2) levels of theory, with extrapolation to the complete basis set limit.
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Lefebvre-Brion, H., & Majumder, M. (2015). Isotopic dependence of the predissociations of the E(1)Pi state of CO. J Chem Phys, 142(16), 164306.
Résumé: The predissociations of the E(1)Pi state of CO are again studied. They include both the background predissociation attributed to the continuum of the A(1)Pi state and the accidental predissociation due to the k(3)Pi state. They are calculated using a coupled equations method. The three components of the k state are introduced. These predissociations are studied for different isotopologues and are shown to decrease with increasing reduced mass, in agreement with the experimental results of Ubachs et al. [J. Chem. Phys. 113, 547 (2000)].
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Martin-Drumel, M. - A., Mouret, G., Pirali, O., & Cuisset, A. (2015). High-resolution synchrotron far infrared spectroscopy of thionyl chloride: Analysis of the ν3 and ν6 fundamental bands. Spectroscopy with Synchrotron Radiation, 315, 30–36.
Résumé: Thionyl chloride (SOCl2) is a volatile inorganic compounds used extensively in industry. Its monitoring in gas phase is critical both for environmental and defense concerns. Previous high-resolution gas phase spectroscopic studies were focused on the microwave region (below 40GHz) and no rotationally-resolved study of the IR spectrum has been reported to date. We present in this article a rovibrational analysis of the two lowest frequency infrared active bending modes ν3 and ν6 of SOCl2. By means of synchrotron based Fourier-Transform far-infrared spectroscopy on the AILES beamline of the SOLEIL facility, the spectra of the symmetric ν3 (346cm−1) and asymmetric ν6 (283cm−1) fundamental bands have been rotationally resolved and analyzed.
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Martin-Drumel, M. A., Endres, C. P., Zingsheim, O., Salomon, T., van Wijngaarden, J., Pirali, O., Gruet, S., Lewen, F., Schlemmer, S., McCarthy, M. C., & Thorwirth, S. (2015). The SOLEIL view on sulfur rich oxides: The S2O bending mode ν2 at 380cm−1 and its analysis using an Automated Spectral Assignment Procedure (ASAP). Spectroscopy with Synchrotron Radiation, 315, 72–79.
Résumé: The fundamental vibrational bending mode ν2 of disulfur monoxide, S2O, and the associated hot band 2ν2-ν2 have been observed at high spectral resolution for the first time at the SOLEIL synchrotron facility using Fourier-transform far-infrared spectroscopy. This transient species has been produced in a radio-frequency discharge by flowing SO2 over elemental sulfur. The spectroscopic analysis has been performed using the newly developed Automated Spectral Assignment Procedure (ASAP) which has enabled the accurate determination of more than 3500 energy levels of the v2=1and2 vibrational states. The procedure provides a fast and convenient way to analyze large data sets in a straightforward manner, if one of the two vibrational states involved in the transition is accurately known from prior work. In addition to the high-resolution synchrotron study, pure rotational spectra of S2O in the v2=1 and 2 vibrational states were observed in the frequency range 250–500GHz by absorption spectroscopy in a long-path absorption cell. From these combined measurements, extensive molecular parameter sets have been determined, including full sets of sextic and two octic centrifugal distortion terms. Highly accurate band centers (to better than 10-5cm−1) have been derived for both vibrational bands.
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Pirali, O., & Boudon, V. (2015). Synchrotron-based Fourier transform spectra of the ν23 and ν24 IR bands of hexamethylenetetramine C6N4H12. Spectroscopy with Synchrotron Radiation, 315, 37–40.
Résumé: Hexamethylenetetramine (HMT), C6N4H12 is a spherical top with nine IR-active modes. Because of its relevance for astrophysics, we recorded the absorption spectra in the full range of its fundamental bands. In total, we detected eight fundamental bands and recently published the rotational analysis of the four most intense bands (ν19,ν20,ν21,ν22) located in the 1000–1500cm−1 range as a support for astronomical searches (Pirali et al., 2014). While the CH stretch modes are unresolved broad features, in this article we report the analysis of the two remaining fundamental bands exhibiting rotationally resolved structures: ν23–GS and ν24–GS located at about 820cm−1 and 670cm−1, respectively.
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Pirali, O., Kisiel, Z., Goubet, M., Gruet, S., Martin-Drumel, M. A., Cuisset, A., & Hindle, F. and M., G. (2015). Rotation-vibration interactions in the spectra of polycyclic aromatic hydrocarbons: Quinoline as a test-case species. Journal of Chemical Physics, 142(10), 104310.
Résumé: Polycyclic aromatic hydrocarbons (PAHs) are highly relevant for astrophysics as possible, though controversial, carriers of the unidentified infrared emission bands that are observed in a number of different astronomical objects. In support of radio-astronomical observations, high resolution laboratory spectroscopy has already provided the rotational spectra in the vibrational ground state of several molecules of this type, although the rotational study of their dense infrared (IR) bands has only recently become possible using a limited number of experimental set-ups. To date, all of the rotationally resolved data have concerned unperturbed spectra. We presently report the results of a high resolution study of the three lowest vibrational states of quinoline C9H7N, an N-bearing naphthalene derivative. While the pure rotational ground state spectrum of quinoline is unperturbed, severe complications appear in the spectra of the nu(45) and nu(44) vibrational modes (located at about 168 cm(-1) and 178 cm(-1), respectively). In order to study these effects in detail, we employed three different and complementary experimental techniques: Fourier-transform microwave spectroscopy, millimeter-wave spectroscopy, and Fourier-transform far-infrared spectroscopy with a synchrotron radiation source. Due to the high density of states in the IR spectra of molecules as large as PAHs, perturbations in the rotational spectra of excited states should be ubiquitous. Our study identifies for the first time this effect and provides some insights into an appropriate treatment of such perturbations.
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Schubert, A., Falvo, C., & Meier, C. (2015). Vibrational-coherence measurement of nonequilibrium quantum systems by four-wave mixing. Phys. Rev. A, 92, 053402.
Résumé: We show theoretically that a quantum system in a nonequilibrium state interacting with a set of laser pulses in a four-wave-mixing setup leads to signal emission in directions opposite to the ones usually considered. When combined with a pump mechanism which sets a time origin for the nonequilibrium state creation, this particular optical response can be utilized to directly follow decoherence processes in real time. By varying the time delays within the probe sequence, signals in these unconventional directions can also be used to detect two-dimensional spectra determined by the dynamics of up to three-quantum coherences, revealing energetical anharmonicities and environmental influences. As a numerical example, these findings are demonstrated by considering a model of vibrational decoherence of carbon monoxide after photolysis from a hemeprotein.
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Tammaro, S., Pirali, O., Roy, P., Lampin, J. - F., Ducourneau, G., Cuisset, A., Hindle, F., & Mouret, G. (2015). High density THz frequency comb produced by coherent synchrotron radiation. Nat. Commun., 6, 7733.
Résumé: Frequency combs have enabled significant progress in frequency metrology and high-resolution spectroscopy extending the achievable resolution while increasing the signal-to-noise ratio. In its coherent mode, synchrotron radiation is accepted to provide an intense terahertz continuum covering a wide spectral range from about 0.1 to 1 THz. Using a dedicated heterodyne receiver, we reveal the purely discrete nature of this emission. A phase relationship between the light pulses leads to a powerful frequency comb spanning over one decade in frequency. The comb has a mode spacing of 846 kHz, a linewidth of about 200 Hz, a fractional precision of about 2 × 10^{−10} and no frequency offset. The unprecedented potential of the comb for high-resolution spectroscopy is demonstrated by the accurate determination of pure rotation transitions of acetonitrile.
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Tran, H., Vander Auwera, J., Landsheere, X., Ngo, N. H., Pangui, E., Morales, S. B., El Hamzaoui, H., Capoen, B., Bouazaoui, M., Boulet, C., & Hartmann, J. - M. (2015). Infrared light on molecule-molecule and molecule-surface collisions. PRA, 92(1), 012707.
Résumé: By analyzing measured infrared absorption of pure CH4 gas under both “free” (large sample cell) and “confined” (inside the pores of a silica xerogel sample) conditions we give a demonstration that molecule-molecule and molecule-surface collisions lead to very different propensity rules for rotational-state changes. Whereas the efficiency of collisions to change the rotational state (observed through the broadening of the absorption lines) decreases with increasing rotational quantum number J for CH4-CH4 interactions, CH4-surface collisions lead to J-independent linewidths. In the former case, some (weak) collisions are inefficient whereas, in the latter case, a single collision is sufficient to remove the molecule from its initial rotational level. Furthermore, although some gas-phase collisions leave J unchanged and only modify the angular momentum orientation and/or symmetry of the level (as observed through the spectral effects of line mixing), this is not the case for the molecule-surface collisions since they always change J (in the studied J=0–14 range).
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Turowski, M., Crepin, C., Douin, S., & Kolos, R. (2015). Formation and Spectroscopy of Dicyanotriacetylene (NC8N) in Solid Kr. Journal Of Physical Chemistry A, 119(11), 2701–2708.
Résumé: Thermally induced creation of dicyanotriacetylene (NC8N) was observed in solid krypton. Samples were obtained by cryogenic trapping of gaseous cyanoacetylene/Kr mixtures subjected to electric discharges. Strong a (3)Sigma(+)(u) -> X (1)Sigma(+)(g) phosphorescence of NC8N is reported here for the first time; its vibronic structure permitted the measurement of several ground-state vibrational frequencies. Other chemical species, mostly smaller than the precursor molecule, have also been formed, among them the dicarbon molecule (C-2), and these may serve as indispensable building blocks in the NC8N synthesis. Processes leading to the elongation of cyanoacetylenic chains are of potential importance for the chemistry of icy grains present in the interstellar gas clouds.
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Wakelam, V., Loison, J. C., Herbst, E., Pavone, B., Bergeat, A., Béroff, K., Chabot, M., Faure, A., Galli, D., Geppert, W. D., Gerlich, D., Gratier, P., Harada, N., Hickson, K. M., Honvault, P., Klippenstein, S. J., Le Picard, S. D., Nyman, G., Ruaud, M., Schlemmer, S., Sims, I. R., Talbi, D., Tennyson, J., & and Wester, R. (2015). The 2014 KIDA Network for Interstellar Chemistry. The Astrophysical Journal Supplement Series, 217(2), 20.
Résumé: Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011.
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Chapitres de Livres |
Giesen, T. R., G.A., Maier, J. P., Carpentier, Y., Rouillé, G., Steglich, M., Jäger, C., Henning, T., Huisken, F., Oomens, J., Pirali, O., Tielens, A. G. G. M. and Müller, H. S. P. (2015). In Wiley-VCH (Ed.), Molecular Spectroscopy In Laboratory Astrochemistry. From Molecules through Nanoparticles to Grains (pp. 13–108).
Résumé: pp. 13–108 Wiley-VCH, 2015 – ISBN: 9783527408894 (Print) – ISBN: 9783527653133 (Online)
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