Peer-reviewed Publications |
Asselin, P., Madebene, B., Soulard, P., Georges, R., Goubet, M., Huet, T. R., Pirali, O., & Zehnacker-Rentien, A. (2016). Competition between inter- and intra-molecular hydrogen bonding: An infrared spectroscopic study of jet-cooled amino-ethanol and its dimer. Journal Of Chemical Physics, 145(22), 224313.
Résumé: The Fourier transform IR vibrational spectra of amino-ethanol (AE) and its dimer have been recorded at room temperature and under jet-cooled conditions over the far and mid infrared ranges (50-4000 cm(-1)) using the White-type cell and the supersonic jet of the Jet-AILES apparatus at the synchrotron facility SOLEIL. Assignment of the monomer experimental frequencies has been derived from anharmonic frequencies calculated at a hybrid CCSD(T)-F12/MP2 level. Various thermodynamical effects in the supersonic expansion conditions including molar dilution of AE and nature of carrier gas have been used to promote or not the formation of dimers. Four vibrational modes of the observed dimer have been unambiguously assigned using mode-specific scaling factors deduced from the ratio between experimental and computed frequencies for the monomer. The most stable g 'Gg' monomer undergoes strong deformation upon dimerization, leading to a homochiral head to head dimer involving two strong hydrogen bonds. Published by AIP Publishing.
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Broquier, M., Soorkia, S., Dedonder-Lardeux, C., Jouvet, C., Theule, P., & Gregoire, G. (2016). Twisted Intramolecular Charge Transfer in Protonated Amino Pyridine. J. Phys. Chem. A, 120(21), 3797–3809.
Résumé: The excited state properties of protonated ortho (2-), meta (3-), and para (4-) aminopyridine molecules have been investigated through UV photofragmentation spectroscopy and excited state coupled-cluster CC2 calculations. Cryogenic ion spectroscopy allows recording well-resolved vibronic spectroscopy that can be reproduced through Franck-Condon simulations of the pipi* local minimum of the excited state potential energy surface. The excited state lifetimes have also been measured through a pump-probe excitation scheme and compared to the estimated radiative lifetimes. Although protonated aminopyridines are rather simple aromatic molecules, their deactivation mechanisms are indeed quite complex with unexpected results. In protonated 3- and 4-aminopyridine, the fragmentation yield is negligible around the band origin, which implies the absence of internal conversion to the ground state. Besides, a twisted intramolecular charge transfer reaction is evidenced in protonated 4-aminopyridine around the band origin, while excited state proton transfer from the pyridinic nitrogen to the adjacent carbon atom opens with roughly 500 cm-1 of excess energy.
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Capello, M. C., Hernandez, F. J., Broquier, M., Dedonder-Lardeux, C., Jouvet, C., & Pino, G. A. (2016). Hydrogen bonds vs. pi-stacking interactions in the p-aminophenol ... p-cresol dimer: an experimental and theoretical study. Physical Chemistry Chemical Physics, 18(45), 31260–31267.
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Carcabal, P., Descamps, D., Petit, S., Mairesse, Y., Blanchet, V., & Cireasa, R. (2016). Using high harmonic radiation to reveal the ultrafast dynamics of radiosensitiser molecules. Faraday Discussions, 194, 407–425.
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De la Lande, A., Ha-Thi, M. H., Chen, S. F., Soep, B., & Shafizadeh, N. (2016). Structure of cobalt protoporphyrin chloride and its dimer, observation and DFT modeling. Phys. Chem. Chem. Phys., 18(25), 16700–16708.
Résumé: In this article we present a joint study by time-of-flight mass spectroscopy and density functional theory of cobalt protoporphyrin dimer complexes. The main novelty of the experimental part is to reveal the formation of porphyrin dimers that eventually include a chlorine atom. Density functional theory calculations have been performed to shed light on the structural and electronic properties of monomers and dimers that may be formed experimentally. Various geometries of the monomers are analyzed in the two lowest spin states. The electronic structures are examined by means of population analysis relying on the iterative Hirshfeld scheme and the topological analyses of the electron localization function. It is shown that the cobalt ligand bond is purely ionic in the triplet states but shows a noticeable covalent character in the singlet state. Ionization potential of Co-protoporphyrin and binding energies of the chlorine ligand are also reported. Concerning the dimers, several association patterns are investigated for the chlorinated and non-chlorinated complexes. It is found that the structures of the most stable complexes involve four hydrogen bonds between the carboxylic acid moieties of the protoporphyrins. However other association modes are likely to be possible in the experiments.
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Gans, B., Lamarre, N., Broquier, M., Liévin, J., & Boyé-Péronne, S. (2016). Experimental and ab initio characterisation of HC3N+ vibronic structure: II- High-resolution VUV PFI-ZEKE spectroscopy. JOURNAL OF CHEMICAL PHYSICS, 145, 234309.
Résumé: VUV pulsed-field-ionization zero-kinetic-energy photoelectron spectra of X+ 2Π ←X 1Σ+ and B+ 2Π ← X 1Σ+ transitions of the HC14N and HC15N isotopologues of cyanoacetylene have been recorded. The resolution of the photoelectron spectra allowed to resolve the vibrational structures and the spin-orbit splittings in the
cation. Accurate values of the adiabatic ionization potentials of the two isotopologues (E /hc(HC14N) = 93909(2) cm−1 and E /hc(HC15N) = 93912(2) cm−1), the vibrational frequencies of the ν2, ν6, and ν7 vibrational modes, and the spin-orbit coupling constant (ASO = −44(2) cm−1) of the X+ 2Π cationic ground state have been derived from the measurements. Using ab initio calculations, the unexpected structure of the B+ 2Π ← X 1Σ+ transition is tentatively attributed to a conical intersection between the A+ and B+ electronic states of the cation.
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Gutierrez-Quintanilla, A., Chevalier, M., & Crepin, C. (2016). Double deuterated acetylacetone in neon matrices: infrared spectroscopy, photoreactivity and the tunneling process. Phys Chem Chem Phys, 18(30), 20713–20725.
Résumé: The effect of deuteration of acetylacetone (C5O2H8) is explored by means of IR spectroscopy of its single and double deuterated isotopologues trapped in neon matrices. The whole vibrational spectra of chelated enols are very sensitive to the H-D exchange of the hydrogen atom involved in the internal hydrogen bond. UV excitation of double deuterated acetylacetone isolated in neon matrices induces the formation of four open enol isomers which can be divided into two groups of two conformers, depending on their formation kinetics. Within each group, one conformer is more stable than the other: slow conformer interconversion due to a tunneling process is observed in the dark at low temperature. Moreover, IR laser irradiation at the OD stretching overtone frequency is used to induce interconversion either from the most stable to the less stable conformer or the opposite, depending on the excitation wavelength. The interconversion process is of great help to assign conformers which are definitively identified by comparison between experimental and calculated IR spectra. Kinetic constants of the tunneling process at play are theoretically estimated and agree perfectly with experiments, including previous experiments with the totally hydrogenated acetylacetone.
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Kumar, S., Lucas, B., Fayeton, J., Scuderi, D., Alata, I., Broquier, M., Le Barbu-Debus, K., Lepere, V., & Zehnacker, A. (2016). Photofragmentation mechanisms in protonated chiral cinchona alkaloids. Phys. Chem. Chem. Phys., 18(32), 22668–22677.
Résumé: The photo-stability of protonated cinchona alkaloids is studied in the gas phase by a multi-technique approach. A multi-coincidence technique is used to demonstrate that the dissociation is a direct process. Two dissociation channels are observed. They result from the C-8-C-9 cleavage, accompanied or not by hydrogen migration. The branching ratio between the two photo-fragments is different for the two pseudo-enantiomers quinine and quinidine. Mass spectrometry experiments coupling UV photo-dissociation of the reactants and structural characterization of the ionic photo-products by Infra-Red Multiple Photo-Dissociation (IRMPD) spectroscopy provide unambiguous information on their structure. In addition, quantum chemical calculations allow proposing a reactive scheme and discussing it in terms of the ground-state geometry of the reactant.
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Lamarre, N., Gans, B., Vieira Mendes L.A., Gronowski, M., Guillemin, J. - C., de Oliveira N., Douin, S., Chevalier, M., Crépin, C., Kolos, R., & Boyé-Péronne, S. (2016). Excited electronic structure of methylcyanoacetylene probed by VUV Fourier-transform absorption spectroscopy. JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, 182, 286–295.
Résumé: High resolution photoabsorption spectrum of gas-phase methylcyanoacetylene (CH3C N) has been recorded from 44 500 to 130 000 cm-1 at room temperature with a vacuum ultraviolet Fourier-transform spectrometer on the DESIRS synchrotron beamline (SOLEIL). The absolute photoabsorption cross section in this range is reported for the first time. Valence shell transitions and Rydberg series converging to the ground state X+ 2E of the cation as well as series converging to electronically excited states (A+ 2 A1 and C+) are observed and assigned. Time-dependent density-functional-theory calculations have been performed to support the assignment of the experimental spectrum in the low energy range. A tentative scaling of the previously measured CH3C3N ion yield by Lamarre et al. [17] is proposed, based on the comparison of the absorption data above the first ionization potential with the observed autoionization structures.
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Lepere, V., Le Barbu-Debus, K., Clavaguera, C., Scuderi, D., Piani, G., Simon, A. L., Chirot, F., MacAleese, L., Dugourd, P., & Zehnacker, A. (2016). Chirality-dependent structuration of protonated or sodiated polyphenylalanines: IRMPD and ion mobility studies. Phys. Chem. Chem. Phys., 18(3), 1807–1817.
Résumé: Ion mobility experiments are combined with Infra-Red Multiple Photon Dissociation (IRMPD) spectroscopy and quantum chemical calculations for assessing the role of chirality in the structure of protonated and sodiated di- or tetra-peptides. Sodiated systems show a strong chirality dependence of the competition between Na+...O and Na+...pi interactions. Chirality effects are more subtle in protonated systems and manifest themselves by differences in the secondary interactions such hydrogen bonds between neutral groups or those involving the aromatic rings.
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Lozada-Garcia, R., Mu, D., Plazanet, M., & Carcabal, P. (2016). Molecular gels in the gas phase? Gelator-gelator and gelator-solvent interactions probed by vibrational spectroscopy. Physical Chemistry Chemical Physics, 18(32), 22100–22107.
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Pino, G. A., Feraud, G., Broquier, M., Gregoire, G., Soorkia, S., Dedonder, C., & Jouvet, C. (2016). Non-radiative processes in protonated diazines, pyrimidine bases and an aromatic azine. Phys. Chem. Chem. Phys., 18(30), 20126–20134.
Résumé: The excited state lifetimes of DNA bases are often very short due to very efficient non-radiative processes assigned to the pipi*-npi* coupling. A set of protonated aromatic diazine molecules (pyridazine, pyrimidine and pyrazine C4H5N2+) and protonated pyrimidine DNA bases (cytosine, uracil and thymine), as well as the protonated pyridine (C5H6N+), have been investigated. For all these molecules except one tautomer of protonated uracil (enol-keto), electronic spectroscopy exhibits vibrational line broadening. Excited state geometry optimization at the CC2 level has been conducted to find out whether the excited state lifetimes measured from line broadening can be correlated to the calculated ordering of the pipi* and npi* states and the pipi*-npi* energy gap. The short lifetimes, observed when one nitrogen atom of the ring is not protonated, can be rationalized by relaxation of the pipi* state to the npi* state or directly to the electronic ground state through ring puckering.
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Soorkia, S., Broquier, M., & Gregoire, G. (2016). Multiscale excited state lifetimes of protonated dimethyl aminopyridines. Phys. Chem. Chem. Phys., 18(34), 23785–23794.
Résumé: The excited state dynamics of protonated ortho (2-) and para (4-) dimethyl aminopyridine molecules (DMAPH(+)) has been studied through pump-probe photofragmentation spectroscopy and excited state coupled-cluster CC2 calculations. Multiscale temporal dynamics has been recorded over 9 orders of magnitude from subpicosecond to millisecond. The initially locally excited pipi* state rapidly decays within about 100 fs into a charge transfer state following 90 degrees twist motion of the dimethyl amino group. While this twisted intramolecular charge transfer (TICT) state does not trigger any fragmentation, it selectively leads to specific two-color photofragments through absorption of the probe photon at 355 nm. Besides, the optically dark TICT state provides an efficient deactivation path with high intersystem probability to non-dissociative long-lived triplet states. Such a multiscale pump-probe photodissociation scheme paves the way to systematic studies of charge transfer reactions in the excited state of cold ionic systems stored in a cryogenic cooled ion trap and probed continuously up to the millisecond time scale.
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Thon, R., Chin, W., Chamma, D., Galaup, J. - P., Ouvrard, A., Bourguignon, B., & Crépin, C. (2016). Vibrational spectroscopy and dynamics of W(CO)6in solid methane as a probe of lattice properties. J. Chem. Phys., 145(21), 214306.
Résumé: Methane solids present more than one accessible crystalline phase at low temperature at zero pressure. We trap W(CO)6 in CH4 and CD4 matrices between 8 and 35 K to probe the interaction between an impurity and its surrounding molecular solid under various physical conditions. Linear and nonlinear vibrational spectroscopies of W(CO)6 highlight different kinds of interaction and reveal new and remarkable signatures of the phase transition of methane. The structures in the absorption band of the antisymmetric CO stretching mode exhibit a clear modification at the transition between phase II and phase I in CH4 and motional narrowing is observed upon temperature increase. The vibrational dynamics of this mode is probed in stimulated photon echo experiments performed with a femtosecond IR laser. A short component around 10 ps is detected in the population relaxation lifetime in the high temperature phase of solid CH4 (phase I) and disappears at lower temperatures (phase II) where the vibrational lifetime is in the hundreds of ps. The analysis of the nonlinear time-resolved results suggests that the short component comes from a fast energy transfer between the vibrational excitation of the guest and the lattice in specific families of sites. Such fast transfers are observed in the case of W(CO)6 trapped in CD4 because of an energy overlap of the excitation of W(CO)6 and a lattice vibron. In solid CH4, even when these V-V transfers are not efficient, pure dephasing processes due to the molecular nature of the host occur: they are temperature dependent without a clear modification at the phase transition.
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