Peer-reviewed Publications |
Alekseyev, A. B., Liebermann, H. - P., Vazquez, G. J., & Lefebvre-Brion, H. (2018). Coupled-channel study of the Rydberg-valence interaction in HBr. J Chem Phys, 148(8), 084302.
Résumé: We report an ab initio study of the low-lying valence and Rydberg states of HBr. The calculations are carried out employing the multireference single- and double-excitation configuration interaction method including the spin-orbit interaction. The first excited adiabatic potential of (1)Sigma(+) symmetry presents two minima which correspond to the Rydberg E(1)Sigma(+) and valence V(1)Sigma(+) observed states. We calculate the vibrational levels of these two states using a coupled-channel treatment based on the two diabatic potentials deduced from the ab initio adiabatic potentials and the Rydberg-valence interaction. The chaotic energy separations between the observed levels are well reproduced in the calculations. We have also obtained for the first time theoretical data for numerous Rydberg states of HBr lying in the (66-79) x 10(3) cm(-1) excitation energy interval. The calculated spectroscopic parameters are found to be in good agreement with experiment and provide a basis for future studies of radiative and non-radiative processes in the HBr molecule.
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Augé, B., Been, T., Boduch, P., Chabot, M., Dartois, E., Madi, T., Ramillon, J. M., Ropars, F., Rothard, H., & Voivenel, P. (2018). IGLIAS: A new experimental set-up for low temperature irradiation studies at large irradiation facilities. Review of Scientific Instruments, 89(7), 075105.
Résumé: We designed and built a mobile experimental set-up for studying the interaction of ion beams with solid samples in a wide temperature range from 9 to 300 K. It is either possible to mount up to three samples prepared ex situ or to prepare samples by condensation of molecules from gases or vapours onto IR or Visible-ultraviolet (Vis-UV) transparent windows. The physico-chemical evolution during irradiation can be followed in situ with different analysis techniques including Fourier transform infrared spectroscopy, Vis-UV, and quadrupole mass spectrometry.
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Baraban, J. H., Martin-Drumel, M. - A., Changala, B., Eibenberger, S., Nava, M., Patterson, D., Stanton, J. F., Ellison, G. B., & McCarthy, M. C. (2018). The Molecular Structure of gauche-1,3-Butadiene: Experimental Establishment of Non-planarity. ANGEWANDTE CHEMIE, 57(7), 1821–1825.
Résumé: The planarity of the second stable conformer of 1,3-butadiene, the archetypal diene for the Diels–Alder reaction in which a planar conjugated diene and a dienophile combine to form a ring, is not established. The most recent high level calculations predicted the species to adopt a twisted, gauche structure owing to steric interactions between the inner terminal hydrogens rather than a planar, cis structure favored by the conjugation of the double bonds. The structure cis-1,3-butadiene is unambiguously confirmed experimentally to indeed be gauche with a substantial dihedral angle of 34°, in excellent agreement with theory. Observation of two tunneling components indicates that the molecule undergoes facile interconversion between two equivalent enantiomeric forms. Comparison of experimentally determined structures for gauche- and trans-butadiene provides an opportunity to examine the effects of conjugation and steric interactions.
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Battandier, M., Bonal, L., Quirico, E., Beck, P., Engrand, C., Duprat, J., & Dartois, E. (2018). Characterization of the organic matter and hydration state of Antarctic micrometeorites: A reservoir distinct from carbonaceous chondrites. Icarus, 306, 74–93.
Résumé: This work presents a multi-analysis on 35 Antarctic micrometeorites (AMMs) (Concordia collection 2006) by coupled Raman and Infrared (IR) spectroscopies, in comparison with samples from type 1 and 2 carbonaceous CM, CR and CI chondrites. We identified the Raman G- and D-bands revealing the presence of polyaromatic carbonaceous material on raw particles in a subset of 16 particles. Thirteen AMMs (10 Fg + 1 Fg-Sc + 1 Sc) were selected from this first subset, and analyzed by infrared microscopy along with 4 AMMs (2 Fg + 1 Fg-Sc + 1 Sc) from a previous study by Dobrica et al. (2011). These analyses showed that scoriaceous, fine-grained scoriaceous and part of the fine-grained AMMs are not hydrated, with a weak abundance of carbonaceous matter. According to the Raman criterion defined by Dobrica et al. (2011), hydrous AMMs do not show structural modifications induced by heating through the atmospheric entry. In several hydrous AMMs, the carbonaceous matter abundance is found larger than in Orgueil (CI), Murchison (CM) and QUE 99177 (CR) chondrites and their mineral content exhibit differences reflected by the structure of the silicate 10 µm band. These observations suggest that part of the AMMs originates from one, or several, distinct parent bodies with respect to primitive carbonaceous chondrites. Each hydrous Fg-AMMS displays higher CH2/CH3 ratio and a smaller carbonyl abundance than chondrites, which point toward a mild processing during atmospheric entry, possibly oxidation, which did not modify the carbon backbone and therefore do not induce differences in Raman spectroscopy.
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Coudert, L. H. (2018). Optimal control of the orientation and alignment of an asymmetric-top molecule with terahertz and laser pulses. Journal of Chemical Physics, 148(9), 094306.
Résumé: Quantum optimal control theory is applied to determine numerically the terahertz and nonresonant laser pulses leading, respectively, to the highest degree of orientation and alignment of the asymmetric-top H2S molecule. The optimized terahertz pulses retrieved for temperatures of zero and 50 K lead after 50 ps to an orientation with ⟨ΦZx⟩ = 0.959 73 and ⟨⟨ΦZx⟩⟩ = 0.742 30, respectively. For the zero temperature, the orientation is close to its maximum theoretical value; for the higher temperature, it is below the maximum theoretical value. The mechanism by which the terahertz pulse populates high lying rotational levels is elucidated. The 5 ps long optimized laser pulse calculated for a zero temperature leads to an alignment with ⟨Φ2Zy⟩=0.94416
⟨ΦZy2⟩=0.944 16 and consists of several kick pulses with a duration of ≈0.1 ps. It is found that the timing of these kick pulses is such that it leads to an increase of the rotational energy of the molecule. The optimized laser pulse retrieved for a temperature of 20 K is 6 ps long and yields a lower alignment with ⟨⟨Φ2Zy⟩⟩=0.71720
⟨⟨ΦZy2⟩⟩=0.717 20.
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Coudert, L. H., Gans, B., Garcia, G. A., & Loison, J. - C. (2018). Renner-Teller effects in the photoelectron spectra of CNC, CCN, and HCCN. Journal of Chemical Physics, 148(5), 054302.
Résumé: The line intensity of photoelectron spectra when either the neutral or cationic species display a Renner-Teller coupling is derived and applied to the modeling of the photoelectron spectra of CNC, CCN, and HCCN. The rovibronic energy levels of these three radicals and of their cations are investigated starting from ab initio results. A model treating simultaneously the bending mode and the overall rotation is developed to deal with the quasilinearity problem in CNC+, CCN+, and HCCN and accounts for the large amplitude nature of their bending mode. This model is extended to treat the Renner-Teller coupling in CNC, CCN, and HCCN+. Based on the derived photoelectron line intensity, the photoelectron spectra of all three molecules are calculated and compared to the experimental ones.
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Coudert, L. H., Gans, B., Holzmeier, F., Loison, J. - C., Garcia, G. A., Alcaraz, C., Lopes, A., & Röder, A. (2018). Experimental and theoretical threshold photoelectron spectra of methylene. The Journal of Chemical Physics, 149(22), 224304.
Résumé: The threshold photoelectron spectrum of methylene (CH2), produced by consecutive H atom abstractions on methane, has been recorded using synchrotron radiation. The experimental spectrum spans the region of the X+ 2Πu ← X 3B1 ionizing transition. It is modeled starting from ab initio bending potentials and using the bending approach introduced by Coudert et al. [J. Chem. Phys. 148, 054302 (2018)] accounting for the quasilinearity of CH2 and the strong Renner-Teller interaction in CH2+. This first calculation yields a theoretical threshold photoelectron spectrum which is in moderate agreement with the experimental one. A more accurate approach treating the three vibrational modes is developed for computing the threshold photoelectron spectrum of triatomic C2v molecules. This new treatment is tested modeling the already measured threshold photoelectron spectrum of the X+ 2Πu ← X 1A1 ionizing transition of the water molecule. The threshold photoelectron spectrum of CH2 computed with the new approach compares more favorably with the experimental spectrum and yields an adiabatic ionization potential of 10.386(6) eV.
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Dartois, E., Chabot, M., Id Barkach, T., Rothard, H., Augé, B., Agnihotri, A. N., Domaracka, A., & Boduch, P. (2018). Cosmic ray sputtering yield of interstellar H2O ice mantles. A&A, 618, A173.
Résumé: Aims. Interstellar grain mantles present in dense interstellar clouds are in constant exchange with the gas phase via accretion and desorption mechanisms such as UV, X-ray photodesorption, cosmic ray induced sputtering, grain thermal fluctuations, and chemical reaction energy release. The relative importance of the various desorption mechanisms is of uttermost importance for astrophysical models to constrain the chemical evolution in such high density dense cloud regions.
Methods. The sputtering yields for swift ions simulating the effects of cosmic rays are most often measured in the semi-infinite limit using thick ice targets with the determination of the effective yield per incident ion. In this experimental work we investigated the sputtering yield as a function of ice mantle thickness, exposed to Xe ions at 95 MeV. The ion induced ice phase transformation and the sputtering yield were simultaneously monitored by infrared spectroscopy and mass spectrometry.
Results. The sputtering yield is constant above a characteristic ice layer thickness and then starts to decrease below this thickness. An estimate of the typical sputtering depth corresponding to this length can be evaluated by comparing the infinite thickness yield to the column density where the onset of the sputtering yield decrease occurs. In these experiments the measured characteristic desorption depth corresponds to ≈30 ice layers. Assuming an effective cylindrical shape for the volume of sputtered molecules, the aspect ratio is close to unity; in the semi-infinite ice film case this ratio is the diameter to height of the cylinder. This result shows that most ejected molecules arise from a rather compact volume. The measured infinite thickness sputtering yield for water ice mantles scales as the square of the ion electronic stopping power (Se, deposited energy per unit path length). Considering the experiments on insulators, we expect that the desorption depth dependence varies with Seα, where α ~ 1. Astrophysical models should take into account the thickness dependence constraints of these ice mantles in the interface regions when ices are close to their extinction threshold. In the very dense cloud regions, most of the water ice mantles are above this limit for the bulk of the cosmic rays.
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Dartois, E., Chabot, M., Id Barkach, T., Rothard, H., Augé, B., Agnihotri, A. N., Domaracka, A., & Boduch, P. (2018). Cosmic ray sputtering yield of interstellar H2O ice mantles. A&A, 618.
Résumé: Aims. Interstellar grain mantles present in dense interstellar clouds are in constant exchange with the gas phase via accretion and desorption mechanisms such as UV, X-ray photodesorption, cosmic ray induced sputtering, grain thermal fluctuations, and chemical reaction energy release. The relative importance of the various desorption mechanisms is of uttermost importance for astrophysical models to constrain the chemical evolution in such high density dense cloud regions.
Methods. The sputtering yields for swift ions simulating the effects of cosmic rays are most often measured in the semi-infinite limit using thick ice targets with the determination of the effective yield per incident ion. In this experimental work we investigated the sputtering yield as a function of ice mantle thickness, exposed to Xe ions at 95 MeV. The ion induced ice phase transformation and the sputtering yield were simultaneously monitored by infrared spectroscopy and mass spectrometry.
Results. The sputtering yield is constant above a characteristic ice layer thickness and then starts to decrease below this thickness. An estimate of the typical sputtering depth corresponding to this length can be evaluated by comparing the infinite thickness yield to the column density where the onset of the sputtering yield decrease occurs. In these experiments the measured characteristic desorption depth corresponds to ≈30 ice layers. Assuming an effective cylindrical shape for the volume of sputtered molecules, the aspect ratio is close to unity; in the semi-infinite ice film case this ratio is the diameter to height of the cylinder. This result shows that most ejected molecules arise from a rather compact volume. The measured infinite thickness sputtering yield for water ice mantles scales as the square of the ion electronic stopping power (Se, deposited energy per unit path length). Considering the experiments on insulators, we expect that the desorption depth dependence varies with Seα, where α ~ 1. Astrophysical models should take into account the thickness dependence constraints of these ice mantles in the interface regions when ices are close to their extinction threshold. In the very dense cloud regions, most of the water ice mantles are above this limit for the bulk of the cosmic rays.
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Dartois, E., Engrand, C., Duprat, J., Godard, M., Charon, E., Delauche, L., Sandt, C., & Borondics, F. (2018). Dome C ultracarbonaceous Antarctic micrometeorites. A&A, 609.
Résumé: Context. UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) represent a small fraction of interplanetary dust particles reaching the Earth’s surface and contain large amounts of an organic component not found elsewhere. They are most probably sampling a contribution from the outer regions of the solar system to the local interplanetary dust particle (IDP) flux.
Aims. We characterize UCAMMs composition focusing on the organic matter, and compare the results to the insoluble organic matter (IOM) from primitive meteorites, IDPs, and the Earth.
Methods. We acquired synchrotron infrared microspectroscopy (μFTIR) and μRaman spectra of eight UCAMMs from the Concordia/CSNSM collection, as well as N/C atomic ratios determined with an electron microprobe.
Results. The spectra are dominated by an organic component with a low aliphatic CH versus aromatic C=C ratio, and a higher nitrogen fraction and lower oxygen fraction compared to carbonaceous chondrites and IDPs. The UCAMMs carbonyl absorption band is in agreement with a ketone or aldehyde functional group. Some of the IR and Raman spectra show a C≡N band corresponding to a nitrile. The absorption band profile from 1400 to 1100 cm-1 is compatible with the presence of C-N bondings in the carbonaceous network, and is spectrally different from that reported in meteorite IOM. We confirm that the silicate-to-carbon content in UCAMMs is well below that reported in IDPs and meteorites. Together with the high nitrogen abundance relative to carbon building the organic matter matrix, the most likely scenario for the formation of UCAMMs occurs via physicochemical mechanisms taking place in a cold nitrogen rich environment, like the surface of icy parent bodies in the outer solar system. The composition of UCAMMs provides an additional hint of the presence of a heliocentric positive gradient in the C/Si and N/C abundance ratios in the solar system protoplanetary disc evolution.
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F Calvo and P Parneix and C Falvo. (2018). Atomistic modeling of the infrared response of fullerenes under hydrostatic pressure. Journal of Physics: Condensed Matter, 30(47), 474001.
Résumé: The anharmonic infrared spectrum of individual C 60 and C 70 fullerenes under hydrostatic pressure was theoretically computed by means of atomistic simulations. Using a tight-binding model for the fullerenes and a simple particle-based pressure-transmitting fluid, the structural and vibrational properties were determined at room temperature and up to 20 GPa. All properties generally exhibit relative variations that are linear with increasing pressure, but whose magnitude can be comparable to pure thermal effects. The bond length contraction usually agrees with existing results, and for C 70 our approach manages to reproduce the occasionally negative pressure coefficient found for some low-frequency modes in experiments.
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Falvo, C. (2018). Linear and non-linear infrared response of one-dimensional vibrational Holstein polarons in the anti-adiabatic limit: Optical and acoustical phonon models. The Journal of Chemical Physics, 148(7), 074103.
Résumé: The theory of linear and non-linear infrared response of vibrational Holstein polarons in one-dimensional lattices is presented in order to identify the spectral signatures of self-trapping phenomena. Using a canonical transformation, the optical response is computed from the small polaron point of view which is valid in the anti-adiabatic limit. Two types of phonon baths are considered: optical phonons and acoustical phonons, and simple expressions are derived for the infrared response. It is shown that for the case of optical phonons, the linear response can directly probe the polaron density of states. The model is used to interpret the experimental spectrum of crystalline acetanilide in the C=O range. For the case of acoustical phonons, it is shown that two bound states can be observed in the two-dimensional infrared spectrum at low temperature. At high temperature, analysis of the time-dependence of the two-dimensional infrared spectrum indicates that bath mediated correlations slow down spectral diffusion. The model is used to interpret the experimental linear-spectroscopy of model α-helix and β-sheet polypeptides. This work shows that the Davydov Hamiltonian cannot explain the observations in the NH stretching range.
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Falvo, C., Gamboa-Suárez, A., Cazayus-Claverie, S., Parneix, P., & Calvo, F. (2018). Isomerization kinetics of flexible molecules in the gas phase: Atomistic versus coarse-grained sampling. The Journal of Chemical Physics, 149(7), 072334.
Résumé: Isomerization kinetics of molecules in the gas phase naturally falls on the microcanonical ensemble of statistical mechanics, which for small systems might significantly differ from the more traditional canonical ensemble. In this work, we explore the examples of cis-trans isomerization in butane and bibenzyl and to what extent the fully atomistic rate constants in isolated molecules can be reproduced by coarse-graining the system into a lower dimensional potential of mean force (PMF) along a reaction coordinate of interest, the orthogonal degrees of freedom acting as a canonical bath in a Langevin description. Time independent microcanonical rate constants can be properly defined from appropriate state residence time correlation functions; however, the resulting rate constants acquire some time dependence upon canonical averaging of initial conditions. Stationary rate constants are recovered once the molecule is placed into a real condensed environment pertaining to the canonical ensemble. The effective one-dimensional kinetics along the PMF, based on appropriately chosen inertia and damping parameters, quantitatively reproduces the atomistic rate constants at short times but deviates systematically over long times owing to the neglect of some couplings between the system and the bath that are all intrinsically present in the atomistic treatment. In bibenzyl, where stronger temperature effects are noted than in butane, the effective Langevin dynamics along the PMF still performs well at short times, indicating the potential interest of this extremely simplified approach for sampling high-dimensional energy surfaces and evaluating reaction rate constants.
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Floß, J., Boulet, C., Hartmann, J. - M., Milner, A. A., & Milner, V. (2018). Electronic spin polarization with an optical centrifuge. Physical Review A, 98(4), 043401.
Résumé: We investigate, both theoretically and experimentally, the mechanism behind the creation of a macroscopic magnetization in a gas of paramagnetic molecules with an optical centrifuge, reported in [Phys. Rev. Lett. 118, 243201 (2017)]. Our analysis shows that the centrifuged super-rotors and noncentrifuged molecules are polarized in opposite directions, while the net magnetic moment of the whole ensemble at the end of the interaction with the laser pulse remains close to zero. As the super-rotors are more stable against reorienting collisions, their spin polarization, which points along the centrifuge axis, decays more slowly than the oppositely oriented polarization of the noncentrifuged molecules. The latter lose their directional rotation much more quickly and with it the polarization of their electronic spin. We show numerically that owing to this difference in decay rates, a net magnetization in the direction of the centrifuge is generated. The proposed model is supported by experimental data.
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Garcia, G. A., Gans, B., Kruger, J., Holzmeier, F., Roder, A., Lopes, A., Fittschen, C., Alcaraz, C., & Loison, J. - C. (2018). Valence shell threshold photoelectron spectroscopy of C3Hx (x = 0-3). Phys. Chem. Chem. Phys., 20, 8707–8718.
Résumé: We present the photoelectron spectra of C3Hx (x = 0-3) formed in a microwave discharge flow-tube reactor by consecutive H abstractions from C3H4 (C3Hx + F [rightward arrow] C3Hx-1 + HF (x = 1-4)), but also from F + CH4 schemes by secondary reactions. The spectra were obtained combining tunable VUV synchrotron radiation with double imaging electron/ion coincidence techniques, yielding mass-selected threshold photoelectron spectra. The obtained results complement not only existing ones, but for the first time the photoelectron spectra of C3, cyclic and linear C3H (c,l-C3H) as well as of the excited states of C3H3 are reported. In the case of c-C3H, l,t-C3H2 and C3H3, Franck-Condon simulations have been performed in order to assign the vibrational structure. The adiabatic ionization energies of these radicals are reported and compared to ab initio calculated values as well as to theoretical values using known enthalpies of formation.
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Ha-Thi, M. - H., Pham, V. - T., Pino, T., Maslova, V., Quaranta, A., Lefumeux, C., Leiblc, W., & and Aukauloo, A. (2018). Photoinduced electron transfer in a molecular dyad by nanosecond pump–pump–probe spectroscopy. Photochem. Photobiol. Sci., 17, 903–909.
Résumé: The design of robust and inexpensive molecular photocatalysts for the conversion of abundant stable molecules like H2O and CO2 into an energetic carrier is one of the major fundamental questions for scientists nowadays. The outstanding challenge is to couple single photoinduced charge separation events with the sequential accumulation of redox equivalents at the catalytic unit for performing multielectronic catalytic reactions. Herein, double excitation by nanosecond pump–pump–probe experiments was used to interrogate the photoinduced charge transfer and charge accumulation on a molecular dyad composed of a porphyrin chromophore and a ruthenium-based catalyst in the presence of a reversible electron acceptor. An accumulative charge transfer state is unattainable because of rapid reverse electron transfer to the photosensitizer upon the second excitation and the low driving force of the forward photodriven electron transfer reaction. Such a method allows the fundamental understanding of the relaxation mechanism after two sequential photon absorptions, deciphering the undesired electron transfer reactions that limit the charge accumulation efficiency. This study is a step toward the improvement of synthetic strategies of molecular photocatalysts for light-induced charge accumulation and more generally, for solar energy conversion.
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Hartmann, J. - M., Boulet, C., Tran, D. D., Tran, H., & Baranov, Y. (2018). Effect of humidity on the absorption continua of CO2 and N2 near 4 μm: Calculations, comparisons with measurements, and consequences for atmospheric spectra. Journal of Chemical Physics, 148(5), 054304.
Résumé: We present a theoretical study of the effects of collisions with water vapor molecules on the absorption, around 4 μm, in both the high frequency wing of the CO2 ν3 band and the collision-induced fundamental band of N2. Calculations are made for the very first time, showing that predictions based on classical molecular dynamics simulations enable, without adjustment of any parameter, very satisfactory agreement with the few available experimental determinations. This opens the route for a future study in which accurate temperature-dependent (semi-empirical) models will be built and checked through comparisons between computed and measured atmospheric spectra. This is of interest since, as demonstrated by simulations, neglecting the humidity of air can lead to significant modifications of the atmospheric transmission (and thus also emission) between 2000 and 2800 cm−1.
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Hartmann, J. - M., Boulet, C., Zhang, H., Billard, F., Faucher, O., & Lavorel, B. (2018). Collisional dissipation of the laser-induced alignment of ethane gas: A requantized classical model. The Journal of Chemical Physics, 149(15), 154301.
Résumé: We present the first theoretical study of collisional dissipation of the alignment of a symmetric-top molecule (ethane gas) impulsively induced by a linearly polarized non-resonant laser field. For this, Classical Molecular Dynamics Simulations (CMDSs) are carried out for an ensemble of C2H6 molecules based on knowledge of the laser-pulse characteristics and on an input intermolecular potential. These provide, for a given gas pressure and initial temperature, the orientations of all molecules at all times from which the alignment factor is directly obtained. Comparisons with measurements show that these CMDSs well predict the permanent alignment induced by the laser pulse and its decay with time but, as expected, fail in generating alignment revivals. However, it is shown that introducing a simple requantization procedure in the CMDS “creates” these revivals and that their predicted dissipation decay agrees very well with measured values. The calculations also confirm that, as for linear molecules, the permanent alignment of ethane decays more slowly than the transient revivals. The influence of the intermolecular potential is studied as well as that of the degree of freedom associated with the molecular rotation around the symmetry axis. This reveals that ethane practically behaves as a linear molecule because the intermolecular potential is only weakly sensitive to rotation around the C–C axis.
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Hartmann, J. - M., Boulet, C., Zhang, H., Billard, F., Faucher, O., & Lavorel, B. (2018). Collisional dissipation of the laser-induced alignment of ethane gas: Energy corrected sudden quantum model. The Journal of Chemical Physics, 149(21), 214305.
Résumé: We present the first quantum mechanical model of the collisional dissipation of the alignment of a gas of symmetric-top molecules (ethane) impulsively induced by a linearly polarized non-resonant laser field. The approach is based on use of the Bloch model and of the Markov and secular approximations in which the effects of collisions are taken into account through the state-to-state rates associated with exchanges among the various rotational states. These rates are constructed using the Energy Corrected Sudden (ECS) approximation with (a few) input parameters obtained independently from fits of the pressure-broadening coefficients of ethane absorption lines. Based on knowledge of the laser pulse characteristics and on these rates, the time-dependent equation driving the evolution of the density matrix during and after the laser pulse is solved and the time dependence of the so-called “alignment factor” is computed. Comparisons with measurements, free of any adjusted parameter, show that the proposed approach leads to good agreement with measurements. The analysis of the ECS state-to-state collisional rates demonstrates that, as in the case of linear molecules, collision-induced changes of the rotational angular momentum orientation are slower than those of its magnitude. This explains why the collisional decay of the permanent component of the alignment is significantly slower than that of the amplitudes of the transient revivals in both experimental and computed results. It is also shown that, since intermolecular forces within C2H6 colliding pairs weakly depend on rotations of the molecules around their C–C bond, the dissipation mechanism of the alignment in pure ethane is close to that involved in linear molecules.
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Hartmann, J. - M., Tran, H., Armante, R., Boulet, C., Campargue, A., Forget, F., Gianfrani, L., Gordon, I., Guerlet, S., Gustafsson, M., Hodges, J. T., Kassi, S., Lisak, D., Thibault, F., & Toon, G. C. (2018). Recent advances in collisional effects on spectra of molecular gases and their practical consequences. Journal of Quantitative Spectroscopy and Radiative Transfer, 213, 178–227.
Résumé: We review progress, since publication of the book “Collisional effects on molecular spectra: Laboratory experiments and models, consequences for applications” (Elsevier, Amsterdam, 2008), on measuring, modeling and predicting the influence of pressure (ie of intermolecular collisions) on the spectra of gas molecules. We first introduce recently developed experimental techniques of high accuracy and sensitivity. We then complement the above mentioned book by presenting the theoretical approaches, results and data proposed (mostly) in the last decade on the topics of isolated line shapes, line-broadening and -shifting, line-mixing, the far wings and associated continua, and collision-induced absorption. Examples of recently demonstrated consequences of the progress in the description of spectral shapes for some practical applications (metrology, probing of gas media, climate predictions) are then given. Remaining issues and directions for future research are finally discussed.
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Heays, A. N., de Oliveira, N., Gans, B., Ito, K., Boyé-Péronne, S., Douin, S., Hickson, K. M., Nahon, L., & and Loison, J. C. (2018). High-resolution one-photon absorption spectroscopy of the D 2S- <- X 2Pi system of radical OH and OD. Journal of Quantitative Spectroscopy and Radiative Transfer, 204, 12–22.
Résumé: Vacuum-ultraviolet (VUV) photoabsorption spectra were recorded of the A(v=0) <-X(v=0), D(v=0)<-X(v=0) and D(v=1) <-X(v=0) bands of the OH and OD radicals generated in a plasma-discharge source using synchrotron radiation as a background continuum coupled with the VUV Fourier-transform spectrometer on the DESIRS beamline of synchrotron SOLEIL. High-resolution spectra permitted the quantification of transition frequencies, relative f-values, and natural line broadening. The f -values were absolutely calibrated with respect to a previous measurement of A(v=0) <-X(v=0) [C. C. Wang, D. K. Killinger, Effect of rotational excitation on the band oscillator strength of OH, Phys. Rev. A 20 (1979) 1495–1498.]. Lifetime broadening of the excited D(v=0) and D(v=1) levels is measured for the first time and compared with previous experimental limits, and implies a lifetime 5 times shorter than a theoretical prediction [M. P. J. van der Loo, G. C. Groenenboom, Ab initio calculation of (2+1)
resonance enhanced multiphoton ionization spectra and lifetimes of the (D,3) states of OH and OD, J. Chem. Phys. 123 (7) (2005) 074310.]. A local perturbation of the D(v=0) level in OH was found.
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IdBarkach, T., Mahajan, T., Chabot, M., Béroff, K., Aguirre, N. F., Diaz-Tendero, S., Launoy, T., Padellec, A. L., Perrot, L., Bonnin, M. A., Le, K. C., Geslin, F., de Séréville, N., Hammache, F., Jallat, A., Meyer, A., Charon, E., Pino, T., Hamelin, T., & Wakelam, V. (2018). Semiempirical breakdown curves of C2N(+) and C3N(+) molecules; application to products branching ratios predictions of physical and chemical processes involving these adducts. Molecular Astrophysics, 12, 25–32.
Résumé: We constructed semiempirical breakdown curves (BDC) for C2N, C3N, C2N+ and C3N+ molecules. These BDC, which are energy dependent dissociation branching ratios (BR) curves, were used to predict products branching ratios for various processes leading to the formation of C2N(+) and C3N(+) excited adducts. These processes, of astrochemical interest, are neutral-neutral and ion-molecule reactions, dissociative recombination and charge transfer reactions with He+. Model predictions of BR are compared to the literature data and to reported values in the kinetic database for astrochemistry KIDA. With the new BR values, the CnN abundances in cold cores were simulated.
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Joost, M., Nava, M., Transue, W. J., Martin-Drumel, M. - A., McCarthy, M. C., Patterson, D., & Cummins, C. C. (2018). Sulfur monoxide thermal release from an anthracene-based precursor, spectroscopic identification, and transfer reactivity. Proc Natl Acad Sci USA, 115(23), 5866–5871.
Résumé: The generation of highly reactive molecules under controlled conditions is desirable, as it allows exploration of synthetic chemistry and enables spectroscopic studies of such elusive species. We report here on the synthesis and reactivity of a precursor molecule that readily fragments with concomitant expulsion of dinitrogen and anthracene to release the highly reactive sulfur monoxide, a compound of interest for both synthetic chemists and astrochemists.Sulfur monoxide (SO) is a highly reactive molecule and thus, eludes bulk isolation. We report here on synthesis and reactivity of a molecular precursor for SO generation, namely 7-sulfinylamino-7-azadibenzonorbornadiene (1). This compound has been shown to fragment readily driven by dinitrogen expulsion and anthracene formation on heating in the solid state and in solution, releasing SO at mild temperatures (<100 °C). The generated SO was detected in the gas phase by MS and rotational spectroscopy. In solution, 1 allows for SO transfer to organic molecules as well as transition metal complexes.
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Lee, K. L. K., Martin-Drumel, M. - A., Lattanzi, V., McGuire, B. A., Caselli, P., & McCarthy, M. C. (2018). Gas phase detection and rotational spectroscopy of ethynethiol, HCCSH. Molecular Physics, , 1–11.
Résumé: We report the gas-phase detection and spectroscopic characterisation of ethynethiol , a metastable isomer of thioketene using a combination of Fourier-transform microwave and submillimetre-wave spectroscopies. Several a-type transitions of the normal species were initially detected below 40 GHz using a supersonic expansion-electrical discharge source, and subsequent measurement of higher-frequency, b-type lines using double resonance provided accurate predictions in the submillimetre region. With these, searches using a millimetre-wave absorption spectrometer equipped with a radio frequency discharge source were conducted in the range 280-660 GHz, ultimately yielding nearly 100 transitions up to ^rRo(36) and rQo(36). From the combined data set, all three rotational constants and centrifugal distortion terms up to the sextic order were determined to high accuracy, providing a reliable set of frequency predictions to the lower end of the THz band. Isotopic substitution has enabled both a determination of the molecular structure of HCCSH and, by inference, its formation pathway in our nozzle discharge source via the bimolecular radical-radical recombination reaction , which is calculated to be highly exothermic (-477 kJ/mol) using the HEAT345(Q) thermochemical scheme.
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McGuire, B. A., Martin-Drumel, M. - A., Lee, K. L. K., Stanton, J. F., Gottlieb, C. A., & McCarthy, M. C. (2018). Vibrational satellites of C2S, C3S, and C4S: microwave spectral taxonomy as a stepping stone to the millimeter-wave band. Phys. Chem. Chem. Phys., 20(20), 13870–13889.
Résumé: We present a microwave spectral taxonomy study of several hydrocarbon/CS2 discharge mixtures in which more than 60 distinct chemical species, their more abundant isotopic species, and/or their vibrationally excited states were detected using chirped-pulse and cavity Fourier-transform microwave spectroscopies. Taken together, in excess of 85 unique variants were detected, including several new isotopic species and more than 25 new vibrationally excited states of C2S, C3S, and C4S, which have been assigned on the basis of published vibration-rotation interaction constants for C3S, or newly calculated ones for C2S and C4S. On the basis of these precise, low-frequency measurements, several vibrationally exited states of C2S and C3S were subsequently identified in archival millimeter-wave data in the 253-280 GHz frequency range, ultimately providing highly accurate catalogs for astronomical searches. As part of this work, formation pathways of the two smaller carbon-sulfur chains were investigated using 13C isotopic spectroscopy, as was their vibrational excitation. The present study illustrates the utility of microwave spectral taxonomy as a tool for complex mixture analysis, and as a powerful and convenient 'stepping stone' to higher frequency measurements in the millimeter and submillimeter bands.
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Meek, S. A., Hipke, A., Guelachvili, G., Hansch, T. W., & Picque, N. (2018). Doppler-free Fourier transform spectroscopy. Optics Letters, 43(1), 162–165.
Résumé: Sub-Doppler broadband multi-heterodyne spectroscopy is proposed and experimentally demonstrated. Using two laser frequency combs of slightly different repetition frequencies, we have recorded Doppler-free two-photon dual-comb spectra of atomic rubidium resonances of a width of 6 MHz, while simultaneously interrogating a spectral span of 10 THz. The atomic transitions are uniquely identified via the intensity modulation of the observed fluorescence radiation. To the best of our knowledge, these results represent the first demonstration of Doppler-free Fourier transform spectroscopy and extend the range of applications of broadband spectroscopy towards precision nonlinear spectroscopy. (C) 2017 Optical Society of America
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Morán, G., Ramos-Chagas, G., Hugelier, S., Xie, X., Boudjemaa, R., Ruckebusch, C., Sliwa, M., Darmanin, T., Gaucher, A., Prim, D., Godeau, G., Amigoni, S., Guittard, F., & Méallet-Renault, R. (2018). Superhydrophobic polypyrene films to prevent Staphylococcus aureus and Pseudomonas aeruginosa biofilm adhesion on surfaces: high efficiency deciphered by fluorescence microscopy. Photochem. Photobiol. Sci., 17(8), 1023–1035.
Résumé: A blue luminescent and superhydrophobic coating based on an electropolymerized fluorinated-pyrene monomer and its planktonic bacteria and biofilm repellent properties are reported. Two different pathogenic bacterial strains (Gram-positive and Gram-negative) at two different incubation times (2 h planktonic bacterial and 24 h biofilm adhesion) were studied and monitored (analyzed) using multicolor scanning confocal fluorescence microscopy. The coating was proved to reduce bacterial adhesion by 65%. It is highly effective against biofilm attachment, with 90% reduction of bacteria surface coverage. This blue fluorescent surface provides a facile method to characterize the coating, observe the bacterial distribution and quantify the bacterial coverage rate by fluorescence imaging of different colors. Furthermore, the film does not show significant bacterial toxicity during the working incubation times.
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Mulas, G., Falvo, C., Cassam-Chenaï, P., & Joblin, C. (2018). Anharmonic vibrational spectroscopy of polycyclic aromatic hydrocarbons (PAHs). The Journal of Chemical Physics, 149(14), 144102.
Résumé: While powerful techniques exist to accurately account for anharmonicity in vibrational molecular spectroscopy, they are computationally very expensive and cannot be routinely employed for large species and/or at non-zero vibrational temperatures. Motivated by the study of Polycyclic Aromatic Hydrocarbon (PAH) emission in space, we developed a new code, which takes into account all modes and can describe all infrared transitions including bands becoming active due to resonances as well as overtone, combination, and difference bands. In this article, we describe the methodology that was implemented and discuss how the main difficulties were overcome, so as to keep the problem tractable. Benchmarking with high-level calculations was performed on a small molecule. We carried out specific convergence tests on two prototypical PAHs, pyrene (C16H10) and coronene (C24H12), aiming at optimising tunable parameters to achieve both acceptable accuracy and computational costs for this class of molecules. We then report the results obtained at 0 K for pyrene and coronene, comparing the calculated spectra with available experimental data. The theoretical band positions were found to be significantly improved compared to harmonic density functional theory calculations. The band intensities are in reasonable agreement with experiments, the main limitation being the accuracy of the underlying calculations of the quartic force field. This is a first step toward calculating moderately high-temperature spectra of PAHs and other similarly rigid molecules using Monte Carlo sampling.
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Pham, X. Q., Jonusauskaite, L., Depauw, A., Kumar, N., Lefevre, J. P., Perrier, A., Ha-Thi, M. - H., & Leray, I. (2018). New water-soluble fluorescent sensors based on calix[4]arene biscrown-6 for selective detection of cesium. Journal of Photochemistry and Photobiology A: Chemistry, 364, 355–362.
Résumé: Two new fluorescent chemosensors based on calix[4]arene bis(crown-6) bearing coumarin units have been synthesized for the detection of cesium ions in water. The photophysical and complexing properties of these sensors with cesium were investigated using absorption and fluorescence spectroscopies as well as DFT calculations. The coordination of Cs+ by the these ligands induces a better charge transfer between the donor and acceptor groups of the coumarin, resulting in a bathochromic shift in absorption spectra and an enhancement of emission spectra. Both the ligands display an excellent selectivity for Cs+ over other potentially interfering cations such as Na+, Li+, K+, Mg2+, Ca2+ and Sr2+ ions.
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Ramos Chagas, G., Morán Cruz, G., Giraudon-Colas, G., Savina, F., Méallet-Renault, R., Amigoni, S., Guittard, F., & Darmanin, T. (2018). Anti-bacterial and fluorescent properties of hydrophobic electrodeposited non-fluorinated polypyrenes. Applied Surface Science, 452, 352–363.
Résumé: This work uses an innovative strategy to show a combination of highly hydrophobic films with fluorescence and anti-bacterial properties. Pyrene grafted with linear and branched alkyl chains of various length (from C4H9 to C12H25) were electropolymerized and their wetting behavior and surface morphology were first analyzed. The presence of microstructured spherical particles (1 µm) induces a high increase in the surface hydrophobicity (θw,max = 132°) even if the polymers are intrinsically hydrophilic (θY = 79–88°), while the surface oleophobicity decreases. The emission of the pyrene monomers and polymers is in the green region (λem = 479–515 nm) and showed to be related with the size and the architecture of the chain. The differences in the aggregations and interactions of the oligomers induce a blue-shift and a thinner spectral band for the branched pyrenes compared to the linear ones. A crescent batochromic and hypsochromic shift are observed for linear and branched chains, respectively, as the number of carbons increase. The polypyrenes also have a potential application to serve as coatings towards to prevention of biofilm formation. A reduction between 30–70% was observed for the bacterial adhesion and between 91–94% for the biofilm formation for S. aureus and P. aeruginosa strains. Here we showed for the first time that hydrophobic surfaces bearing hydrocarbon chains without fluorine atoms can be used towards to repel bacteria. Furthermore, the pyrene molecules lead to fluorescent and microstructured hydrophobic surfaces by a one-step electropolymerization process and the combination of these properties enhances the range of applications for these surfaces.
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Rivera-Rivera, L. A., McElmurry, B. A., Scott, K. W., Springer, S. D., Lucchese, R. R., Bevan, J. W., Leonov, I. I., & Coudert, L. H. (2018). 6.2 μm spectrum and 6-dimensional morphed potentials of OC-H2O. Chemical Physics, 501(Supplement C), 35–45.
Résumé: Rovibrational transitions associated with tunneling states in the ν5 (water bending) vibration of the OC-H2O complex have been recorded using a supersonic jet mode-hop free quantum cascade laser spectrometer at 6.2 μm. Analysis of the resulting spectra is facilitated by incorporating fits of previously recorded microwave and submillimeter data accounting for Coriolis coupling. The theoretical basis of morphing a 5-D frozen monomers potential was initially developed and then extended to two 6-D morphed potentials. A combination of these spectroscopic results and previous rovibrational data for the ν5 vibration in OC-D2O are then used to generate a 6-D morphed potential surface for the intermolecular and the water bending vibrations. An alternative 6-D morphed potential of the intermolecular and the ν3 (CO stretching) vibrations was also generated. These determined morphed potentials then formed the basis for modeling the dynamics of the complex and prediction of accurate intermolecular rovibrational frequencies of the complex.
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Shafizadeh, N., Boyé-Péronne, S., Soorkia, S., Chen, S., de la Lande, A., Cunha de Miranda, B., Garcia, G. A., Nahon, L., Poisson, L., & Soep, B. (2018). The surprisingly high ligation energy of CO to Ruthenium porphyrins. Phys. Chem. Chem. Phys., 20, 11730–11739.
Résumé: A combined theoretical and experimental approach has been used to investigate the binding energy of a ruthenium metalloporphyrin ligated with CO, ruthenium tetraphenylporphyrin [RuII TPP], in the RuII oxidation degree. Measurements performed with VUV ionization using the DESIRS beamline at Synchrotron SOLEIL led to adiabatic ionization energies of [RuII TPP] and its complex with CO, [RuII TPP–CO], of 6.48
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Tran, T. - T., Ha-Thi, M. - H., Pino, T., Quaranta, A., Lefumeux, C., Leibl, W., & Aukauloo, A. (2018). Snapshots of Light Induced Accumulation of Two Charges on Methylviologen using a Sequential Nanosecond Pump–Pump Photoexcitation. The Journal of Physical Chemistry Letters, 9(5), 1086–1091.
Résumé: Methylviologen (MV2+) is perhaps the most used component as a reversible electron acceptor in photophysical studies. While MV2+ is most commonly implicated as a reversible one-electron mediator, its electrochemical properties clearly evidence two successive one-electron reduction processes. In this report, we have investigated on the light driven two-charge accumulation on MV2+ using a multicomponent system composed of the prototypical molecular photosensitizer [Ru(bpy)3]2+ and MV2+ in the presence of ascorbate as reversible electron donor. The sequential addition of two electrons on the methylviologen was tracked upon sequential excitation of the [Ru(bpy)3]2+ at optimized concentration of the electron acceptor. The charge accumulated state carries an energy of 0.9 eV above the ground state and has a lifetime of ca. 50 μs. We have reached a fairly good global yield of approximately 9% for the two-charge accumulation. This result clearly demonstrates the potential of this simple approach for applications in artificial photosynthesis.
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