Peer-reviewed Publications |
Basire, M., Parneix, P., & Calvo, F. (2008). Quantum anharmonic densities of states using the Wang-Landau method. JOURNAL OF CHEMICAL PHYSICS, 129(8).
Résumé: The Wang-Landau sampling method is adapted to the calculation of quantum densities of states for fully coupled anharmonic systems. The accuracy of the method is illustrated against exact counting for two molecules with separable oscillators, namely, the Zundel complex H(5)O(2)(+) and the Na(11) cluster. Application to the fully coupled naphthalene molecule (C(10)H(8)) reveals significant deviations in the finite temperature thermodynamical properties that are not captured by simple perturbation theory. There are no limitations in the size of the molecules that can be treated with this method. (c) 2008 American Institute of Physics.
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Boye-Peronne, S., & Gauyacq, D. (2008). Photolysis of small hydrocarbons: a source of radicals for the carbon chemistry in space. ACTUALITE CHIMIQUE, (315), X-XV.
Résumé: The carbon chemistry in the interstellar and cometary media is driven by reaction chains initiated by small radicals such as C-2, C2H, or CH. For many years, the different photochemical steps involved in the production of these reactive radicals were not clearly identified. The role of the stable hydrocarbon molecules (acetylene, ethylene, etc.) as mother molecules is no longer subject of debate. This paper illustrates a spectroscopic method aimed to characterise the radical products and to measure their abundance from an irradiation close to the vacuum-ultraviolet flux present in comets or near carbon-rich stars. Experiments performed with a synchrotron radiation source enable to detail the nature of the primary reactions occurring in the gas phase and involving small hydrocarbon mother molecules. The photolysis of acetylene C2H2 and ethylene C2H4 will be shown as an example of this laboratory-based approach.
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Crepin, C., Moneron, L., Douin, S., Boye-Peronne, S., Kolos, R., Turowski, M., Gronowski, M., Sepiol, J., Benilan, Y., & Gazeau, M. - C. (2008). Tentative identification of C3N center dot radical luminescence in solid krypton. POLISH JOURNAL OF CHEMISTRY, 82(4), 741–749.
Résumé: A product of cyanoacetylene photodissociation in Kr matrices gives rise to visible emis-. sion bands tentatively identified as due to the fluorescence and to the phosphorescence of the C3N center dot radical. This assignment, which involves the low-lying (A) over tilde (2) Pi state as the final one for both emissions, is based on the isotopic substitution study and on former theoretical predictions.
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Cuisset, A., Mouret, G., Pirali, O., Roy, P., Cazier, F., Nouali, H., & Demaison, J. (2008). Gas-phase vibrational spectroscopy and ab initio study of organophosphorous compounds: Discrimination between species and conformers. JOURNAL OF PHYSICAL CHEMISTRY B, 112(39), 12516–12525.
Résumé: Gas phase vibrational spectra of dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), and triethyl phosphate (TEP) have been measured using FTIR spectroscopy. For DMMP, TMP, and TEP, most of the infrared active vibrational modes have been observed in the 50-5000 cm(-1) spectral range, allowing an unambiguous discrimination between the three molecules. The vibrational analysis of the spectra was performed by comparing with MP2 and B3LYP harmonic and anharmonic force field ab initio calculations. The extension to anharmonic calculations provides the best agreement for the mid-infrared and the near-infrared spectra, but they do not improve the harmonic frequency predictions in the far-infrared domain. This part of the vibrational spectra associated with collective and nonlocalized vibrational modes presents the largest frequency differences between the two lowest energy conformers of DMMP and TMP. These two conformers were taken into account in the vibrational assignment of the spectra. Their experimental evidence was obtained by deconvoluting vibrational bands in the mid-infrared and in the far-infrared regions, respectively. For TEP, the conformational landscape appears very complicated at ambient temperature, and a further analysis at low temperature is required to explain the vibrational features of each conformer.
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Dozova, N., Murray, C., McCaffrey, J. G., Shafizadeh, N., & Crepin, C. (2008). Amplified emission of phthalocyanine isolated in cryogenic matrices. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 10(16), 2167–2174.
Résumé: Laser induced fluorescence spectroscopy of free-base (H2Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices reveals a quite unexpected phenomenon with a moderate increase in the laser intensity. In all matrices except Xe, a huge increase occurs in the intensity of an emission band near 755 nm when pumping the S-1 <- S-0 transition. The band involves a vibrational mode of the ground state, located at 1550 and 1525 cm(-1) for H2Pc and ZnPc, respectively. Many of the characteristics of amplified emission (AE) are exhibited by this vibronic transition. Excitation scans recorded for the AE band yield greatly enhanced site selectivity compared to what is obtained in normalfluorescence excitation scans.
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Falvo, C., Hayashi, T., Zhuang, W., & Mukamel, S. (2008). Coherent two dimensional infrared spectroscopy of a cyclic decapeptide Antamanide. A simulation study of the amide-I and A bands. JOURNAL OF PHYSICAL CHEMISTRY B, 112(39), 12479–12490.
Résumé: The two-dimensional infrared photon echo spectrum of Antamanide (-(1)Val-(2)Pro-(3)Pro-(4)Ala-(5)Phe-(6)Phe-(7)Pro-(8)Pro-(9)Phe-(10)Pro -) in chloroform is calculated using an explicit solvent molecular dynamics (MD) simulation combined with a density functional theory (DFT) map for the effective vibrational Hamiltonian. Evidence for a strong intramolecular hydrogen bonding network is found. Comparison with experimental absorption allows the identification of the dominant conformation. Multidimensional spectroscopy reveals intramolecular couplings and gives information on its dynamics. A two-color amide-I and amide-A crosspeak is predicted and analyzed in terms of local structure.
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Pino, T., Dartois, E., Cao, A. - T., Carpentier, Y., Chamaille, T., Vasquez, R., Jones, A. P., d'Hendecourt, L., & Brechignac, P. (2008). The 6.2 μm band position in laboratory and astrophysical spectra: a tracer of the aliphatic to aromatic evolution of interstellar carbonaceous dust. ASTRONOMY & ASTROPHYSICS, 490(2), 665–672.
Résumé: Context. The infrared emission features observed in the mid-infrared wavelength range in astronomical objects, often called the Aromatic Infrared Bands, exhibit differences in shape and position. Three astrophysical spectral classes have been proposed based on the spectral characteristics. The band positions in most sources are similar to those of aromatic materials, however, the exact nature of the emitters is still unknown. Aims. The spectral diversity of the bands provides a clue to the nature of the materials. An evolutionary scenario for the nature of the emitters can be inferred by comparison with laboratory analogues. Methods. The laboratory spectra of a wide range of soot material samples were recorded and a global analysis of the infrared absorption spectra performed. This spectral analysis, allied to the band shape and position variations, were then used to interpret the diversity and evolution of the features in the astronomical spectra. Results. We find correlations between the spectral regions characteristic of the CC and CH modes and use these to shed light on the origin of the infrared emission features. In particular, the observed shift in the position of the 6.2-6.3 μm band is shown to be a key tracer of the evolution of the aliphatic to aromatic component of carbonaceous dust.
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Poisson, L., Shafizadeh, N., & Haacke, S. (2008). Femtosecond dynamic of complexe molecules. ACTUALITE CHIMIQUE, (317), 62–64.
Résumé: Electronic relaxation is the first step in photochemistry which either guides these systems into the reacting states or dissipates the energy to form non reactive states and stop photochemistry. This relaxation operates often at femtosecond time scales, driven by molecular movements. It has become possible to explore these relaxation processes in many complex systems by femtosecond pump probe methods to investigate the flux of energy leading to photochemistry or stopping photochemistry. Gas phase methods are specifically interesting to understand the initial processes in these systems, for instance in photochromic molecules and metalloporphyrins. In the liquid phase, femtosecond fluorescence up-conversion methods combine temporal and spectral resolution. This combination offers a clearer picture of the nature of the excited population and its de-excitation.
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Romanzin, C., Gans, B., Douin, S., Boye-Peronne, S., & Gauyacq, D. (2008). 193 nm photolysis of CHCl3: Probe of the CH product by CRDS. CHEMICAL PHYSICS, 351(1-3), 77–82.
Résumé: The CH radical production induced by 193 nm two-photon photolysis ofCHC13 has been measured for the first time via the cavity ring-down absorption spectroscopy of its A-X bands, using a commercial nanosecond pulsed dye laser. The range of pressure and laser intensity, as well as the time window detection, have been carefully chosen to ensure a constant CH number density during the measurement and to avoid post-photolysis reactivity. Internal energy distribution of the CH((XII)-I-2) fragment has been derived from population distribution simulations, leading to an average vibrational temperature T-vib = 1900 +/- 50 K and rotational temperature Tr t = 300 +/- 20 K. Two competing mechanisms can be i nvoked for the CH production channel: either two-photon absorption via resonant excited states of CHCl3 leading to dissociation of excited CHCl3, or two-photon sequential dissociation via the formation of the vibrationally excited CHCl2 fragment. The latter mechanism is proposed to be the prominent process for CH formation. (c) 2008 Elsevier B.V. All rights reserved.
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Shafizadeh, N., Poisson, L., & Soep, B. (2008). Ultrafast electronic relaxation of excited state vitamin B(12) in the gas phase. CHEMICAL PHYSICS, 350(1-3), 2–6.
Résumé: The time evolution of electronically excited vitamin B(12) (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states. (C) 2007 Elsevier B.V. All rights reserved.
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Tuna, T., Chabot, M., Pino, T., Desesquelles, P., Le Padellec, A., Martinet, G., Barat, M., Lucas, B., Mezdari, F., Montagnon, L., Van-Oanh, N. T., Lavergne, L., Lachaize, A., Carpentier, Y., & Beroff, K. (2008). Fragmentation branching ratios of highly excited hydrocarbon molecules C(n)H and their cations C(n)H(+) (n <= 4). JOURNAL OF CHEMICAL PHYSICS, 128(12).
Résumé: We have measured fragmentation branching ratios of neutral C(n)H and C(n)H(+) cations produced in high velocity (4.5 a.u) collisions between incident C(n)H(+) cations and helium atoms. Electron capture gives rise to excited neutral species C(n)H and electronic excitation to excited cations C(n)H(+). Thanks to a dedicated setup, based on coincident detection of all fragments, the dissociations of the neutral and cationic parents were recorded separately and in a complete way. For the fragmentation of C(n)H, the H-loss channel is found to be dominant, as already observed by other authors. By contrast, the H-loss and C-loss channels equally dominate the two-fragment break up of C(n)H(+) species. For these cations, we provide the first fragmentation data (n > 2). Results are also discussed in the context of astrochemistry. (c) 2008 American Institute of Physics.
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Turowski, M., Gronowski, M., Boye-Peronne, S., Douin, S., Moneron, L., Crepin, C., & Kolos, R. (2008). The C(3)N(-) anion: First detection of its electronic luminescence in rare gas solids. JOURNAL OF CHEMICAL PHYSICS, 128(16).
Résumé: The 193 nm laser irradiation of cyanoacetylene (HCCCN) that was isolated in rare gas solids led to a long-lived luminescence (origin at 3.58 eV), which was assigned to the (a) over tilde (3)Sigma(+)-(X) over tilde (1)Sigma(+) system of cyanoacetylide (CCCN(-)). The identification, which involved (15)N and (2)H isotopic substitution studies, is based on vibronic spacings in the phosphorescence spectrum (compared to previous infrared absorption measurements and to theoretical results regarding CCCN(-) vibrational frequencies), as well as on a BD(T)/cc-pVTZ prediction for the singlet-triplet energy gap in this anion (3.61 eV). The same emission was also generated from Kr/HC(3)N mixtures subjected to a glow electric discharge immediately before the solidification (cold-window-radial-discharge technique).
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Actes de Conférences |
Pino, T., Cao, A. T., Carpentier, Y., Dartois, E., d'Hendecourt, L., & Brechignac, P. (2008). Laboratory analogues of hydrocarbonated interstellar nanograins. In IAU: ORGANIC MATTER IN SPACE (Vol. 4, pp. 393–394).
Résumé: Carbonaceous extraterrestrial matter is observed in a wide variety of astrophysical environments. The spectroscopic signatures revealed a large variety of chemical structure illustrating the rich carbon chemistry that occurs in space. In order to produce laboratory analogues of carbonaceous cosmic dust, a new chemical reactor has been built, in the Laboratoire de Photophysique Moleculaire. It is a low pressure flat burner providing flames of premixed hydrocarbon/oxygen gas mixtures, closely following the model system used by the combustion community. hi such a device the flame is a one-dimensional chemical reactor that, offers a broad range of combustion conditions and sampling which allows production of many and various by-products hi the present work, we studied: i) the infrared transmission spectra of thin film deposit samples whose nature ranges from strongly aromatic to strongly aliphatic materials; ii) Hie resonant two-photon photoionisation spectra of gas phase PAHs formed in the flame.
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