Peer-reviewed Publications |
Bagchi, S., Falvo, C., Mukamel, S., & Hochstrasser, R. M. (2009). 2D-IR Experiments and Simulations of the Coupling between Amide-I and Ionizable Side Chains in Proteins: Application to the Villin Headpiece. JOURNAL OF PHYSICAL CHEMISTRY B, 113(32), 11260–11273.
Résumé: The carboxylate side chains of Asp and Glu have significant coupling with the amide states of the backbone of the Villin headpiece. In two-dimensional spectroscopy, cross peaks are observed between these side chains and the main amide-I band. To model the absorption of the side chains, the electric field variations of vibrational frequencies of a carboxylic acid group (neutral form, CH(3)-COOH) and a carboxylate group (ionized form, CH(3)-COO(-)) are parametrized by means of density functional theory calculations. Simulations indicate that the side chains significantly couple to only one or two amide-I modes out of all of the amino acid residues which makes them useful as spectroscopic markers, providing information about the local structural behavior of the protein. Both experiment and simulations show that the cross peaks between the carboxylate and the amide-I bands are significantly diminished above the melting temperature,
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Basire, M., Parneix, P., Calvo, F., Pino, T., & Brechignac, P. (2009). Temperature and Anharmonic Effects on the Infrared Absorption Spectrum from a Quantum Statistical Approach: Application to Naphthalene. JOURNAL OF PHYSICAL CHEMISTRY A, 113(25), 6947–6954.
Résumé: A method is developed to Calculate the finite-temperature infrared absorption spectrum of polyatomic molecules with energy levels described by a second-order Dunham expansion. The anharmonic couplings are fully incorporated in the calculation of the quantum density of states, achieved using a Wang-Landau Monte Carlo procedure, as well as in the determination of transition energies. Additional multicanonical simulations provide the microcanonical absorption intensity as a function of both the absorption wavelength and the internal energy of the molecule. The finite-temperature spectrum is finally obtained by Laplace transformation of this microcanonical histogram. The present scheme is applied to the infrared spectrum of naphthalene, for which we quantity the shifting, broadening, and third-order effects as a continuous function of temperature. The influence of anharmonicity and couplings is manifested on the nontrivial variations of these features with increasing temperature.
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Beroff, K., Chabot, M., Mezdari, F., Martinet, G., Tuna, T., Desesquelles, P., Le Padellec, A., & Barat, M. (2009). Fragmentation of small carbon clusters, a review. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 267(6), 866–871.
Résumé: An overview of the works devoted to fragmentation of small carbon clusters is given in a first part. Fragmentation of swift neutral and (multi) charged carbon clusters studied with the AGAT spectrometer is presented and discussed in a second part. (C) 2009 Elsevier B.V. All rights reserved.
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Brunetto, R., Pino, T., Dartois, E., Cao, A. - T., d'Hendecourt, L., Strazzulla, G., & Brechignac, P. (2009). Comparison of the Raman spectra of ion irradiated soot and collected extraterrestrial carbon. ICARUS, 200(1), 323–337.
Résumé: We use a low pressure flame to produce soot by-products as possible analogues of the carbonaceous dust present in diverse astrophysical environments, such as circumstellar shells, diffuse interstellar medium, planetary disks, as well as in our own Solar System. Several soot samples, displaying an initial chemical diversity from aromatic to aliphatic dominated material, are irradiated with 200-400 keV H(+), He(+), and Ar(++) ions, with fluences comprised between 10(14) and 10(16) ions/cm(2), to simulate expected radiation induced modification on extraterrestrial carbon. The evolution of the samples is monitored using Raman spectroscopy, before, during, and after irradiation. A detailed analysis of the first- and second-order Raman spectra is performed, using a fitting combination of Lorentzian and/or Gaussian-shaped bands. Upon irradiation, the samples evolve toward an amorphous carbon phase. The results suggest that the observed variations are more related to vacancy formation than ionization processes. A comparison with Raman spectra of extraterrestrial organic matter and other irradiation experiments of astrophysically relevant carbonaceous materials is presented. The results are consistent with previous experiments showing mostly amorphization of various carbonaceous materials. Irradiated soots have Raman spectra similar to those of some meteorites, IDPs, and Comet Wild 2 grains collected by the Stardust mission. Since the early-Sun expected irradiation fluxes sufficient for amorphization are compatible with accretion timescales, our results support the idea that insoluble organic matter (IOM) observed in primitive meteorites has experienced irradiation-induced amorphization prior to the accretion of the parent bodies, emphasizing the important role played by early solar nebula processing. (C) 2008 Elsevier Inc. All Fights reserved.
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Calvo, F., & Parneix, P. (2009). Phase Space Theory of Evaporation in Neon Clusters: The Role of Quantum Effects. JOURNAL OF PHYSICAL CHEMISTRY A, 113(52), 14352–14363.
Résumé: Unimolecular evaporation of neon clusters containing between 14 and 148 atoms is theoretically investigated in the framework of phase space theory. Quantum effects are incorporated in the vibrational densities of states, which include both zero-point and anharmonic contributions, and in the possible tunneling through the centrifugal barrier. The evaporation rates, kinetic energy released, and product angular momentum are calculated as a function of excess energy or temperature in the parent cluster and compared to the classical results. Quantum fluctuations are found to generally increase both the kinetic energy released and the angular momentum of the product, but the effects on the rate constants depend nontrivially on the excess energy. These results are interpreted as due to the very few vibrational states available in the product cluster when described quantum mechanically. Because delocalization also leads to much narrower thermal energy distributions, the variations of evaporation observables as a function of canonical temperature appear much less marked than in the microcanonical ensemble. While quantum effects tend to smooth the caloric curve in the product cluster, the melting phase change clearly keeps a signature on these observables. The microcanonical temperature extracted from fitting the kinetic energy released distribution using an improved Arrhenius form further Suggests a backbending in the quantum Ne(13) Cluster that is absent in the classical system. Finally, in contrast to delocalization effects, quantum tunneling through the centrifugal barrier does not play any appreciable role on the evaporation kinetics of these rather heavy clusters.
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Calvo, F., Parneix, P., & Basire, M. (2009). Quantum densities of states of fluxional polyatomic systems from a superposition approximation. JOURNAL OF CHEMICAL PHYSICS, 130(15).
Résumé: The superposition method is used to calculate quantum densities of states of polyatomic systems with multiple isomeric structures. For each isomer, anharmonicities are included rigorously using a Dunham expansion of the vibrational energy levels and short exchange Monte Carlo simulations are used to compute the individual quantum densities of states. The method is applied to the computation of thermodynamical properties of the Ar(13) and Ne(13) clusters. The canonical heat capacities are found in very satisfactory agreement with the predictions of quantum or semiclassical sampling methods.
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Falvo, C., Palmieri, B., & Mukamel, S. (2009). Coherent infrared multidimensional spectra of the OH stretching band in liquid water simulated by direct nonlinear exciton propagation. JOURNAL OF CHEMICAL PHYSICS, 130(18), 184501.
Résumé: The two-dimensional vibrational response of the disordered strongly fluctuating OH exciton band in liquid water is investigated using a new simulation protocol. The direct nonlinear exciton propagation generalizes the nonlinear exciton equations to include nonadiabatic time dependent Hamiltonian and transition dipole fluctuations. The excitonic picture is retained and the large cancellation between Liouville pathways is built-in from the outset. The sensitivity of the photon echo and double-quantum-coherence techniques to frequency fluctuations, molecular reorientation, intermolecular coupling, and the two-exciton coherence is investigated. The photon echo is particularly sensitive to the frequency fluctuations and molecular reorientation, whereas the double-quantum coherence provides a unique probe for intermolecular couplings and two-exciton coherence.
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Laruelle, F., Boye-Peronne, S., Gauyacq, D., & Lievin, J. (2009). Revisiting Mulliken's Concepts about Rydberg States and Rydberg-Valence Interactions from Large-Scale Ab Initio Calculations on the Acetylene Molecule. JOURNAL OF PHYSICAL CHEMISTRY A, 113(47), 13210–13220.
Résumé: A quantitative characterization of the Rydberg and valence singlet electronic states of acetylene lying in the 5-10.7 eV region is performed by using large-scale ab initio calculations. A special attention is paid on the comparison between the present calculations and Mulliken's concepts for Rydberg states, based on single-electron and single-configuration description. Most of the properties of the Rydberg states have been qualitatively understood via this comparison, mainly shown by the shape and size of the outer Rydberg molecular orbital. More quantitatively, Rydberg-valence mixing has been evaluated in several excited energy regions, as for instance, the interaction between the (C) over tilde' (1 pi(g))(2) (1)A(g) doubly excited valence state and the manifold of electronic components of the np series, or the interaction between the (E) over tilde 1 pi(g) (1)B(u) valence state and the (F) over tilde 3d pi(g) (1)Sigma(+)(u) Rydberg state. The rapid predissociation of the lowest (C) over tilde 3s sigma (1)Pi(u) Rydberg state has been interpreted as a case of Rydbergization, earlier predicted by Mulliken.
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Lepere, V., Picard, Y. J., Barat, M., Fayeton, J. A., Lucas, B., & Beroff, K. (2009). Photodissociation dynamics of Ar2(+) and Ar3(+) excited by 527 nm photons. J Chem Phys, 130(19), 194301.
Résumé: The photofragmentation dynamics of Ar(2)(+) and Ar(3)(+) clusters has been investigated at a 527 nm wavelength (2.35 eV) using a setup that allows simultaneous detection of the ionic and neutral fragments in a coincidence experiment. Measurement of positions and times of flight enables in principle a complete description of the fragmentation dynamics. The photofragmentation dynamics of Ar(3)(+) clusters is similar to that of Ar(2)(+) with, in addition, the ejection of a third fragment that can be neutral or ionized via a resonant electron capture. This is attributed to the triangular geometry of the Ar(3)(+) ion.
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Pirali, O., Tokaryk, D. W., & Vervloet, M. (2009). Vibrational dependence of the rotational, spin-orbit splitting, and lambda-doubling parameters in the C ''(5)Pi(ui) state of N-2. CANADIAN JOURNAL OF PHYSICS, 87(5), 601–606.
Résumé: We have recorded the high-resolution emission spectrum of the Herman infrared band (C ''(5)Pi(ui)-A'(5)Sigma(+)(g)) system of N-2 in the 8000-15000 cm(-1) range from an experimental set-up coupling a corona discharge with a supersonic expansion. The analysis of four new bands has permitted us to determine spectroscopic parameters of the nu' = 0 and nu' = 1 vibrational levels of the C ''(5)Pi(ui) state and to study the vibrational dependence of the molecular parameters over the range nu' = 0 to v' = 4. In particular, the values of the spin-orbit coupling and the Lambda-doubling parameters are discussed.
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Pirali, O., Vervloet, M., Mulas, G., Malloci, G., & Joblin, C. (2009). High-resolution infrared absorption spectroscopy of thermally excited naphthalene. Measurements and calculations of anharmonic parameters and vibrational interactions. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 11(18), 3443–3454.
Résumé: We report in this paper the recording and analysis of the vibrational spectrum of naphthalene in the 1.6-200 μm (50-6000 cm(-1)) spectral range with a resolution of 0.005 cm(-1). The spectrum, recorded at room temperature, shows several complex structures in the Q branches of the c-type bands, which can be assigned to hot-band sequences as well as combination bands and overtones. To analyse the experimental data, we developed a model based on anharmonic calculations which predicts the transitions (positions and intensities) involving the vibrational levels populated at room temperature. This work permits us to estimate the validity and limitations of our calculations, which can be used to predict the band profiles of naphthalene (and larger PAHs) at various temperatures, with potential astrophysical applications.
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Schmidt, T. W., Pino, T., & Brechignac, P. (2009). The C-H Stretch Intensities of Polycyclic Aromatic Hydrocarbon Cations. Origins and Astrophysical Implications. JOURNAL OF PHYSICAL CHEMISTRY A, 113(15), 3535–3541.
Résumé: Infrared vibrational transition intensities of polycyclic aromatic hydrocarbons are known to depend strongly on the charge state. The detailed understanding of this effect for the C-H stretching modes has been approached by applying the quantum theory of atoms in molecules. Several benchmark calculations were undertaken in order to disentangle charge and size effects, from benzene (C(6)H(6)) up to the ovalene (C(32)H(14)) molecule. Upon decomposition of the dipole moment derivative along a C-H stretch into charge, charge flux, and dipole flux terms, it is found that it is the competition between the sum of the first two terms and the latter which drives the intensity, due to their opposing signs. Additionally, while the dipole flux term changes very little with size and charge, the other terms are strongly sensitive to these. This effect leads to a very weak C-H stretch intensity for cation sizes close to pyrene (C(16)H(10)) and comparable intensities between neutral and cations for the much larger ones. The astrophysical implications are discussed.
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Shafizadeh, N., Soep, B., Mestdagh, J. M., & Breckenridge, W. H. (2009). Charge transfer in metal-atom-containing molecules in the gas phase. INTERNATIONAL REVIEWS IN PHYSICAL CHEMISTRY, 28(3), 359–406.
Résumé: The presence of charge transfer (CT) is ubiquitous in metal-atom-containing molecules in the gas phase. The states of interest range from ground states to the lower excited states, given the generally low ionisation potentials of metal atoms. This review is written from an experimentalist's perspective, to describe the specifics of CT states in stable molecules containing a metal atom or of transient CT states in dynamical processes. The large body of experimental evidence allows the description of such states in an empirical or semi-empirical manner, including partial point charges and polarised electron clouds on the ions. These simple models are compared with more quantitative models, allowing the development of sophisticated descriptions. The simple perspective deriving from experimental evidence is justified, when it is possible via accurate quantum calculations and allows building a rather complete framework for the ionic bond or CT-induced dynamics.
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Actes de Conférences |
Roy, P., Brubach, J. B., Manceron, L., Rouzieres, M., Pirali, O., & Tchana, F. K. (2009). The AILES Beam line for THz and IR spectroscopy. In TERAHERTZ AND MID INFRARED RADIATION: BASIC RESEARCH AND PRACTICAL APPLICATIONS (pp. 63–64).
Résumé: The new infrared beamline (AILES) at the third generation Synchrotron Radiation source SOLEIL is now available for users. This beamline exploits infrared and THz synchrotron radiation from both edge emission and the constant field conventional source. The performances including flux, spatial distribution of the photons, spectral range and stability are discussed and the optical system and spectroscopic stations are described. The combined source with the adapted optics of the beamline offers high flux and brilliance for all kinds of infrared experiments. We will briefly review the main research themes and future developments of coherent emission at SOLEIL.
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