Peer-reviewed Publications |
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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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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Le Barbu-Debus, K., Broquier, M., Mahjoub, A., & Zehnacker-Rentien, A. (2008). Chiral recognition between alpha-hydroxylesters: A double-resonance IR/UV study of the complexes of methyl mandelate with methyl glycolate and methyl lactate. JOURNAL OF PHYSICAL CHEMISTRY A, 112(40), 9731–9741.
Résumé: Chiral recognition between alpha hydroxylesters has been studied in jet-cooled complexes of methyl mandelate with methyl lactate. The complex with nonchiral methyl glycolate has also been studied for the sake of comparison. The hydrogen-bond topology of the complexes has been interrogated by means of IR/UV double-resonance spectroscopy in the range of 3 μm. A theoretical approach has been conducted in conjunction with the experimental work to assist in the analysis of the spectra. Owing to the conformational flexibility of the subunits at play, emphasis has been put on the methodology used for the exploration of the potential-energy surface. The hydrogen-bond topology is very similar in the homo- and heterochiral complexes. It involves insertion of the hydroxyl group of methyl mandelate within the intramolecular hydrogen bond of methyl lactate or methyl glycolate, resulting in a five-membered ring. This contrasts with methyl lactate clusters previously studied by FTIR spectroscopy in a filet jet.(1).
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Lucas, B., Barat, M., Fayeton, J. A., Jouvet, C., Çarçabal, P., & Grégoire, G. (2008). Statistical versus non-statistical photo-fragmentation of protonated GWG tri-peptide induced by UV excitation. Chemical Physics, 347(1-3), 324–330.
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Lucas, B., Barat, M., Fayeton, J. A., Perot, M., Jouvet, C., Gregoire, G., & Brondsted Nielsen, S. (2008). Mechanisms of photoinduced Calpha[Single Bond]Cbeta bond breakage in protonated aromatic amino acids. J Chem Phys, 128(16), 164302.
Résumé: Photoexcitation of protonated aromatic amino acids leads to C(alpha)[Single Bond]C(beta) bond breakage among other channels. There are two pathways for the C(alpha)[Single Bond]C(beta) bond breakage, one is a slow process (microseconds) that occurs after hydrogen loss from the electronically excited ion, whereas the other is a fast process (nanoseconds). In this paper, a comparative study of the fragmentation of four molecules shows that the presence of the carboxylic acid group is necessary for this fast fragmentation channel to occur. We suggest a mechanism based on light-induced electron transfer from the aromatic ring to the carboxylic acid, followed by a fast internal proton transfer from the ammonium group to the negatively charged carboxylic acid group. The ion formed is a biradical since the aromatic ring is ionized and the carbon of the COOH group has an unpaired electron. Breakage of the weak C(alpha)[Single Bond]C(beta) bond gives two even-electron fragments and is expected to quickly occur. The present experimental results together with the ab initio calculations support the interpretation previously proposed.
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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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Zehnacker, A., & Suhm, M. A. (2008). Chirality recognition between neutral molecules in the gas phase. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 47(37), 6970–6992.
Résumé: Noncovalent interactions are particularly intriguing when they involve chiral molecules, because the interactions change in a subtle way upon replacing one of the partners by its mirror image. The resulting phenomena involving chirality recognition are relevant in the biosphere, in organic synthesis, and in polymer design. They may be classified according to the permanent or transient chirality of the interacting partners, leading to chirality discrimination, chirality induction, and chirality synchronization processes. For small molecules, high-level quantum chemical calculations for such processes are feasible. To provide reliable connections between theory and experiment, such phenomena are best studied in vacuum isolation at low temperature, using rotational, vibrational, electronic, and photoionization spectroscopy. We review these techniques and the results which have become available in recent years, with special emphasis on dimers of permanently chiral molecules and on the influence of conformational flexibility. Analogies between the microscopic mechanisms and macroscopic phenomena and between intra- and intermolecular cases are drawn.
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Actes de Conférences |
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Alcaraz, C., Carniato, V., Lecadre, F., Carcabal, P., Broquier, M., Dedonder-Lardeux, C., & Jouvet, C. (2008). A VUV line at the Server Laser at the Paris-Sud University Laser Center. In UVX 2008: 9E COLLOQUE SUR LES SOURCES COHERENTES ET INCOHERENTES UV (pp. 1–6). E D P SCIENCES.
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Cafarelli, P., Carcabal, P., Champeaux, J. - P., Le Padellec, A., Moretto-Capelle, P., Rabier, J., & Sence, M. (2008). Ionization and Fragmentation of 5-Chlorouracil induced by 100 keV protons collisions. In AIP Conference Proceedings (Vol. 1080, pp. 71–77).
Résumé: We present preliminary experimental results on the dissociation of singly and doubly ionized 5-Chlorouracil induced by collisions with proton of 100 keV energy. Multiple coincidence techniques are used to detect the ionic fragments from single dissociation events. This enables a thorough analysis of kinetic momentums of the charged and neutral species involved in the dissociation. In many cases, this leads to the establishment of the scenario the molecule undergoes after ionization as well as the determination of the nature of intermediate (undetected) species. In other cases, the dissociation scenario cannot be unambiguously identified and further analysis as well as theoretical support is needed.
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