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31 results on '"Astrochimie expérimentale"'

1. Characterization of circumstellar carbonaceous dust analogues produced by pyrolysis of acetylene in a porous graphite reactor

Author

Robert Georges, Bertrand R. Rowe, Elangannan Arunan, Ludovic Biennier, Thierry Bataille, Vijayanand Chandrasekaran, V. Jayaram, K. P. J. Reddy, Astrochimie expérimentale, Physique des atomes, lasers, molécules et surfaces (PALMS), Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique de Rennes (IPR), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences Chimiques de Rennes (ISCR), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Solid State and Structural Chemistry Unit, Indian Institute of Science, Department of Aerospace Engineering, Inorganic and Physical Chemistry (IPC), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Analytical chemistry, chemistry.chemical_element, Infrared spectroscopy, 02 engineering and technology, 01 natural sciences, 7. Clean energy, Fourier transform spectroscopy, law.invention, chemistry.chemical_compound, law, 0103 physical sciences, Physics::Atomic and Molecular Clusters, General Materials Science, Graphite, Physics::Chemical Physics, Spectroscopy, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Graphene, General Chemistry, [PHYS.ASTR.SR]Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], 021001 nanoscience & nanotechnology, chemistry, Acetylene, 0210 nano-technology, Carbon, Pyrolysis
Abstract

International audience; Carbon particles synthesized by acetylene pyrolysis in a porous graphite reactor have been investigated. The intimate chemical and physical structures of the particles were probed by proton nuclear magnetic resonance spectroscopy, infrared Fourier transform spectroscopy and X-ray diffraction. The analysis points towards a chemical structure composed of soluble low-mass aromatics surrounding small insoluble larger aromatic islands bridged by aliphatic groups. The diffraction profile indicates that the particles are mostly amorphous with small crystalline domains of ∼6.5 Å composed of a few stacked graphene layers. The properties of these particles are compared with these obtained with other types of production methods such as laser pyrolysis and combustion flames. The results are briefly discussed in the context of the evolution of infrared interstellar emitters. Possible uses of the reactor are proposed.

Published
2009
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2. Gas-Phase Infrared Spectra of Vinyl Selenol and Vinyl Tellurol

Author

Brahim Khater, Abdessamad Benidar, Jean-Claude Guillemin, Manuel Yáñez, José A. Gámez, Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences Chimiques de Rennes (ISCR), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Synthèses et activations de biomolécules (SAB), Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Centre National de la Recherche Scientifique (CNRS), Departemento de Química C-9, Universidad Autónoma de Madrid (UAM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Centre National de la Recherche Scientifique (CNRS)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR), and Universidad Autonoma de Madrid (UAM)

Subjects
Vinyl alcohol, Vinyl Compounds, Vapor pressure, Infrared spectroscopy, 010402 general chemistry, Photochemistry, Vibration, 01 natural sciences, chemistry.chemical_compound, Coordination Complexes, Organoselenium Compounds, Spectroscopy, Fourier Transform Infrared, 0103 physical sciences, [CHIM]Chemical Sciences, Computer Simulation, Physical and Theoretical Chemistry, 010306 general physics, Conformational isomerism, Basis set, Selenol, Hydrogen atom, 0104 chemical sciences, Models, Chemical, chemistry, Quantum Theory, Physical chemistry, Density functional theory, Gases
Abstract

International audience; The infrared spectra (3500-500 cm(-1)) of gaseous vinyl selenol and vinyl tellurol have been recorded at 0.1 cm(-1) resolution. For the latter the spectra were obtained at room temperature, but for the former a temperature of -40 degrees C was required because of the chemical instability of vinyl selenol at room temperature. To compensate the very weak vapor pressure of vinyl tellurol at room temperature, a long optical path up to 136 m was necessary to record its spectrum. B3LYP density functional theory (DFT) calculations have been performed to assign the different absorption bands. Since an unambiguous assignment of the absorption bands requires a precise knowledge on the relative abundance of the syn and gauche rotamers of these compounds, their relative energies and their anharmonic vibrational frequencies were obtained using a very extended Def2-QZVP basis set. Two rotamers, the syn, which is planar, and a nonplanar gauche, were found to be local minima for both compounds. The gauche rotamer presents two degenerate conformers, which differ by the position of the SeH (TeH) hydrogen atom above or below the molecular plane. Our theoretical results are in good agreement with the main features of the experimental spectra. Fundamental bands and some combination bands of vinyl selenol and vinyl tellurol were assigned and compared with those of vinyl alcohol and vinyl thiol, whose spectra had been reported previously in the literature.

Published
2009
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3. Small-angle neutron scattering study of soot particles in an ethylene–air diffusion flame

Author

James Mitchell, J.L. Le Garrec, S. di Stasio, A. I. Florescu-Mitchell, Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Physique des atomes, lasers, molécules et surfaces (PALMS), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Aerosol and Nanostructures Laboratory [Napoli], Consiglio Nazionale delle Ricerche [Napoli] (CNR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
010504 meteorology & atmospheric sciences, General Chemical Engineering, Analytical chemistry, General Physics and Astronomy, Energy Engineering and Power Technology, 02 engineering and technology, Neutron scattering, medicine.disease_cause, complex mixtures, 01 natural sciences, Soot, medicine, Physics::Chemical Physics, 0105 earth and related environmental sciences, SANS, Chemistry, Small-angle X-ray scattering, Diffusion flame, SAXS, General Chemistry, 021001 nanoscience & nanotechnology, Small-angle neutron scattering, Fuel Technology, flame, Nanoparticles, Particle, Particle size, Small-angle scattering, 0210 nano-technology
Abstract

International audience; Neutron scattering techniques have been applied to the study soot particles in an ethylene diffusion flame. Primary particle sizes have been determined as a function of height-above-the-burner. The practicality of the method has been demonstrated.

Published
2006
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4. Direct absorption spectroscopy of water clusters formed in a continuous slit nozzle expansion

Author

Manuel Goubet, Robert Georges, Audrey Moudens, A.A. Vigasin, S.E. Lokshtanov, Jan Makarewicz, Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique des Lasers, Atomes et Molécules - UMR 8523 (PhLAM), Université de Lille-Centre National de la Recherche Scientifique (CNRS), Faculty of Chemistry, Adam Mickiewicz University in Poznań (UAM), Wave Research Center (General Physics Institute), Russian Academy of Sciences [Moscow] (RAS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Absorption spectroscopy, infrared spectra, water, Analytical chemistry, molecular beams, 36.40.Mr Spectroscopy and geometrical structure of clusters, 33.20.Ea Infrared spectra, 33.20.Tp Vibrational analysis, 33.15.Mt Rotation, vibration, and vibration-rotation constants, 31.15.ae Electronic structure and bonding characteristics, 33.15.Fm, General Physics and Astronomy, Infrared spectroscopy, chemistry.chemical_element, 010402 general chemistry, 01 natural sciences, 0103 physical sciences, Cluster (physics), Physics::Atomic and Molecular Clusters, Physical and Theoretical Chemistry, Argon, 010304 chemical physics, Chemistry, Fourier transform spectra, ab initio calculations, Solvation, 0104 chemical sciences, molecular clusters, Solvation shell, argon, hydrogen bonds, Absorption (chemistry), solvation, Water vapor, vibrational states
Abstract

International audience; In this article, we report on a Fourier transform infrared study of absorption bands belonging to small-sized water clusters formed in a continuous slit nozzle expansion of water vapor seeded in argon carrier gas. Clear signatures of free and H-bonded OH vibrations in water aggregates from dimer to pentamer are seen in our spectra. Following an increase in argon backing pressure, the position of the cluster absorption bands varies from those characteristics of isolated water aggregates in the gas phase to those known for clusters trapped in a static argon matrix. These variations can be interpreted in terms of sequential solvation of the water clusters by an increasing number of argon atoms attached to water clusters. Our measured spectra are in good agreement with those obtained previously either for free or Ar coated small-sized water clusters using pulsed slit-jet expansions. Our results are equally in accord with those originating from a variety of tunable laser based techniques using molecular beams or free jets or from the study of water aggregates embedded in rare gas matrices. Distinctions are reported, however, and discussed. Ab initio calculations have made it possible to speculate on the average size of an argon solvation shell around individual clusters as well as on the development of the OH stretch vibrational shifts in mixed (H(2)O)(m)Ar(n) clusters having different compositions and architectures.

Published
2009
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5. Nanoparticle plasma ejected directly from solid copper by localized microwaves

Author

Michael Sztucki, Zahava Barkay, Yariv Shamir, James Mitchell, S. Wonde, J. L. LeGarrec, A. Golts, Noam Eliaz, Dana Ashkenazi, Eli Jerby, Theyencheri Narayanan, Faculty of Engineering, Tel Aviv University (TAU), Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Physique des atomes, lasers, molécules et surfaces (PALMS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), European Synchrotron Radiation Facility (ESRF), Wolfson Applied Materials Research Center, Tel Aviv University [Tel Aviv], Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), and Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
LH, Nanostructure, Materials science, Physics and Astronomy (miscellaneous), Scanning electron microscope, Analytical chemistry, Nanoparticle, chemistry.chemical_element, plasma radiofrequency heating, 02 engineering and technology, 01 natural sciences, Condensed Matter::Materials Science, Condensed Matter::Superconductivity, plasma production, 0103 physical sciences, Nano, Spectroscopy, 010302 applied physics, Scattering, Plasma heating by microwaves, Plasma, X-ray scattering, 021001 nanoscience & nanotechnology, Copper, collisional heating, ECR, chemistry, copper, Physics::Space Physics, nanoparticles, 0210 nano-technology, boundary layer effects, scanning electron microscopy, plasma-wall interactions, Plasma-material interactions
Abstract

International audience; A plasma column ejected directly from solid copper by localized microwaves is studied. The effect stems from an induced hotspot that melts and emits ionized copper vapors as a confined fire column. Nanoparticles of ~20-120 nm size were revealed in the ejected column by in situ small-angle x-ray scattering. Optical spectroscopy confirmed the dominance of copper particles in the plasma column originating directly from the copper substrate. Nano- and macroparticles of copper were verified also by ex situ scanning electron microscopy. The direct conversion of solid metals to nanoparticles is demonstrated and various applications are proposed.

Published
2009
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6. Vibrational spectra of vinylarsine: A joint experimental and anharmonic theoretical study

Author

Claude Pouchan, Jean-Claude Guillemin, Abdessamad Benidar, Rémi Marchal, Didier Bégué, Institut pluridisciplinaire de recherche sur l'environnement et les matériaux (IPREM), Université de Pau et des Pays de l'Adour (UPPA)-Centre National de la Recherche Scientifique (CNRS), Synthèses et activations de biomolécules (SAB), Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences Chimiques de Rennes (ISCR), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Institut Pluridisciplinaire de Recherche sur l'Environnement et les Matériaux (IPREM), Centre National de la Recherche Scientifique (CNRS)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), and Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)

Subjects
010304 chemical physics, Chemistry, Anharmonicity, General Physics and Astronomy, 010402 general chemistry, 01 natural sciences, Molecular physics, Spectral line, 0104 chemical sciences, Gas phase, Variational method, Quantum mechanics, 0103 physical sciences, [CHIM]Chemical Sciences, Physics::Chemical Physics, Physical and Theoretical Chemistry, Joint (geology), Vibrational spectra, Complement (set theory)
Abstract

International audience; A joint experimental and theoretical analyses based on the grounds of DFT anharmonic potential and the use of a variational method allow us to revisit and assign the gas phase spectra of vinylarsine in the mid-IR area until 6300 cm−1. Several weak and very weak bands corresponding to overtones and combinations are newly observed and assigned in complement to the fundamental bands.

Published
2009
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7. Small angle x-ray scattering study of flame soot nanoparticle aggregation and restructuring

Author

A. I. Florescu-Mitchell, S. di Stasio, Theyencheri Narayanan, James Mitchell, J. L. LeGarrec, Michael Sztucki, Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Aerosol and Nanostructures Laboratory [Napoli], Consiglio Nazionale delle Ricerche [Napoli] (CNR), Physique des atomes, lasers, molécules et surfaces (PALMS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), European Synchrotron Radiation Facility (ESRF), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), and Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Integral transforms, restructuring, General Physics and Astronomy, Nanoparticle, 02 engineering and technology, 01 natural sciences, Molecular physics, soot, 010305 fluids & plasmas, symbols.namesake, Flame, X-ray absorption spectra, Optics, 020401 chemical engineering, 0103 physical sciences, 0230Nw , 0230Uu , 7867Bf , 7870Ck , 7870Dm , 8240-g, 0204 chemical engineering, [SPI.NANO]Engineering Sciences [physics]/Micro and nanotechnologies/Microelectronics, Spectroscopy, Nanocrystals and nanoparticles, Scattering, Chemistry, Small-angle X-ray scattering, business.industry, X-ray scattering, XANES, Fourier analysis, Chemical kinetics and reactions: special regimes and techniques, Fourier transform, symbols, aggregates, Particle, nanoparticles, Biological small-angle scattering, business
Abstract

International audience; Results of an in situ small angle x-ray scattering (SAXS) study of soot particles are presented. Scattering data are analyzed using two Fourier transform inversion methods to determine particle volume distributions and by means of the unified function, which allows different structural levels in the scattering objects to be distinguished. We are able to observe the contemporary existence of smaller subprimary particles and larger aggregated particles that usually are classified as primary particles and constitute the building bricks of large fractal-like aggregates with external dimension of above 100 nm. Comparison is made with our previous SAXS and near edge x-ray absorption fine structure spectroscopy results and with those obtained using laser light scattering and particle sampling-electron microscopic methods.

Published
2009
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8. A Short Answer to Critics of Our Article 'Eppur si Espande'

Author

Abramowicz, M. A., Bajtlik, S., Jean-Pierre Lasota, Moudens, A., Copernicus Astronomical Center of the Polish Academy of Sciences (CAMK), Polish Academy of Sciences (PAN), Department of Applied Physics [Gothenburg], Chalmers University of Technology [Göteborg], Institut d'Astrophysique de Paris (IAP), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Astrochimie expérimentale, Laboratoire de Physique Moleculaire pour l'Atmosphere et l'Astrophysique (LPMAA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), and Destouches, Dorothée

Subjects
theory [cosmology], [PHYS.ASTR.SR] Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Cosmology: miscellaneous, [SDU.ASTR.SR] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Astrophysics::Cosmology and Extragalactic Astrophysics, Cosmology: theory, miscellaneous [cosmology], [PHYS.ASTR.SR]Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR]
Abstract

International audience; Recently we presented a formal mathematical proof that, contrary to a widespread misconception, cosmological expansion cannot be understood as the motion of galaxies in non-expanding space. We showed that the cosmological redshift must be physically interpreted as the expansion of space. Although our proof was generally accepted, a few authors disagreed. We rebut their criticism in this Note.

Published
2009

9. Crossed molecular beam study of gas phase reactions relevant to the chemistry of planetary atmospheres: The case of C2+C2H2

Author

Raffaele Petrucci, Paolo Foggi, Nadia Balucani, Piergiorgio Casavecchia, Enrico Segoloni, Francesca Leonori, Sébastien D. Le Picard, Kevin M. Hickson, Dipartimento di Chimica [Perugia], Università degli Studi di Perugia (UNIPG), Institut des Sciences Moléculaires (ISM), Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure de Chimie et de Physique de Bordeaux (ENSCPB)-Université Sciences et Technologies - Bordeaux 1-Université Montesquieu - Bordeaux 4-Institut de Chimie du CNRS (INC), Dipartimento di Chimica, Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Università degli Studi di Perugia = University of Perugia (UNIPG), Université Montesquieu - Bordeaux 4-Université Sciences et Technologies - Bordeaux 1 (UB)-École Nationale Supérieure de Chimie et de Physique de Bordeaux (ENSCPB)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Atmospheres, Gas giant, Experimental techniques, Population, Astrophysics, Jovian planets and Titan Atmospheres, Comets, 01 natural sciences, Crossed molecular beam, symbols.namesake, Reaction rate constant, Planet, 0103 physical sciences, Jovian planets, education, 010303 astronomy & astrophysics, education.field_of_study, 010304 chemical physics, Uranus, Astronomy and Astrophysics, Interstellar medium, 13. Climate action, Space and Planetary Science, symbols, Titan (rocket family), Titan, Composition
Abstract

International audience; The reaction between dicarbon (C2) and acetylene was recently suggested as a possible competitive reaction in the atmospheres of Titan, Saturn and Uranus by rate constant measurements at very low temperatures [see Canosa, A., Páramo, A., Le Picard, S.D., Sims, I.R., 2007. An experimental study of the reaction kinetics of C2(X1Σg+) with hydrocarbons (CH4, C2H2, C2H4, C2H6 and C3H8) over the temperature range 24 300 K: implications for the atmospheres of Titan and the Giant Planets. Icarus 187, 558 568]. We have investigated the reaction of the two low lying electron states of C2 and acetylene by the crossed molecular beam (CMB) technique with mass spectrometric detection. C4H, already identified as a primary product in previous CMB experiments, is confirmed as such, even though the mechanism of formation is inferred to be partly different with respect to the previous study. An experimental setup has been devised to characterize the internal population of C2 and refine the interpretation of the scattering results. The implications for the modelling of the atmospheres of Giant Planets and Titan, as well as cometary comae and the interstellar medium, are discussed.

Published
2008
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10. Absolute cross sections and kinetic energy release distributions for electron-impact dissociative excitation and ionization of NeD+

Author

Jozo Jureta, Pierre Defrance, Julien Lecointre, V. Ngassam, Ann E. Orel, James Mitchell, Département de Physique (PAMO), Université Catholique de Louvain = Catholic University of Louvain (UCL), Institute of Physics, University of Belgrade [Belgrade], Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Department of Applied Science, University of California [Davis] (UC Davis), University of California-University of California, Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), and University of California (UC)-University of California (UC)

Subjects
Physics, [PHYS.PHYS.PHYS-ATM-PH]Physics [physics]/Physics [physics]/Atomic and Molecular Clusters [physics.atm-clus], Ionic bonding, Condensed Matter Physics, Kinetic energy, Threshold energy, 01 natural sciences, Potential energy, Atomic and Molecular Physics, and Optics, Dissociation (chemistry), 010305 fluids & plasmas, Ionization, 0103 physical sciences, Atomic physics, 010306 general physics, 34.80.Gs Molecular excitation and ionization, 34.80.Ht Dissociation and dissociative attachment, Electron ionization, Excitation
Abstract

International audience; Absolute cross sections for electron impact dissociative excitation and ionization of NeD+ leading to the formation of singly and multiply charged products (D+, Ne+, Ne2+ and Ne3+) are reported, in the energy range from their respective thresholds to 2.5 keV. The animated crossed-beams method is used. For singly charged fragments, absolute cross sections are obtained separately for dissociative excitation and for dissociative ionization. Dissociative excitation is seen to be restricted to the low-energy range (

Published
2008
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11. Evidence for nanoparticles in microwave-generated fireballs observed by synchrotron X-ray scattering

Author

Theyencheri Narayanan, J. L. LeGarrec, James Mitchell, Eli Jerby, Michael Sztucki, V. Dikhtyar, Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), European Synchrotron Radiation Facility (ESRF), Faculty of Engineering, Tel Aviv University [Tel Aviv], Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), and Tel Aviv University (TAU)

Subjects
Physics, Dusty plasma, Atmospheric pressure, Scattering, General Physics and Astronomy, 02 engineering and technology, Plasma, 021001 nanoscience & nanotechnology, 01 natural sciences, Synchrotron, law.invention, law, 0103 physical sciences, Particle, Particle size, 52.80.Mg, 52.40.Db, 52.50.Sw, 52.70.La, Small-angle scattering, Atomic physics, 010306 general physics, 0210 nano-technology
Abstract

International audience; The small-angle x-ray scattering method has been applied to study fireballs ejected into the air from molten hot spots in borosilicate glass by localized microwaves [V. Dikhtyar and E. Jerby, Phys. Rev. Lett. 96 045002 (2006)10.1103/PhysRevLett.96.045002]. The fireball's particle size distribution, density, and decay rate in atmospheric pressure were measured. The results show that the fireballs contain particles with a mean size of approximately 50 nm with average number densities on the order of approximately 10(9). Hence, fireballs can be considered as a dusty plasma which consists of an ensemble of charged nanoparticles in the plasma volume. This finding is likened to the ball-lightning phenomenon explained by the formation of an oxidizing particle network liberated by lightning striking the ground [J. Abrahamson and J. Dinniss, Nature (London) 403, 519 (2000)10.1038/35000525].

Published
2008
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12. Electron and ion reactions with hexamethyldisiloxane and pentamethyldisiloxane

Author

Sophie Carles, J. B. A. Mitchell, J.L. Le Garrec, Physique des atomes, lasers, molécules et surfaces (PALMS), Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Astrochimie expérimentale, Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
010302 applied physics, Hexamethyldisiloxane, Argon, Chemistry, Analytical chemistry, General Physics and Astronomy, chemistry.chemical_element, 02 engineering and technology, 021001 nanoscience & nanotechnology, 01 natural sciences, Dissociation (chemistry), Ion, [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, chemistry.chemical_compound, Reaction rate constant, 0103 physical sciences, Mass spectrum, Physical and Theoretical Chemistry, 0210 nano-technology, Chemical decomposition, Dissociative recombination
Abstract

International audience; The dissociative recombination of electrons with the hexamethyldisiloxane (HMDSO) cation ((CH(3))(3)Si-O-Si(CH(3))(3))(+) and the pentamethyldisiloxane cation ((CH(3))(3)Si-O-Si(CH(2))(2))(+) as well as the ion-molecule reaction between Ar(+) and HMDSO have been studied at 300 K using a flowing afterglow Langmuir probe-mass spectrometer apparatus. The rate constants for these reactions, measured directly for the first time, are, respectively, alpha(1)=1.8 x 10(-6), alpha(2)=3.6 x 10(-6) cm(3)s, and k=2.0 x 10(-9) cm(3)s with uncertainties of +/-30%. In addition, the electronic attachment to neutral HMDSO was also studied and an upper limit value of the rate constant was determined to be beta=3.3 x 10(-11) cm(3)s.

Published
2007
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13. Understanding reactivity at very low temperatures: the reactions of oxygen atoms with alkenes

Author

Ian W. M. Smith, Yuri Georgievskii, Ian R. Sims, Stephen J. Klippenstein, Ludovic Biennier, Hassan Sabbah, Physique des atomes, lasers, molécules et surfaces (PALMS), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Astrochimie expérimentale, Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Combustion Research Facility, Sandia National Laboratories - Corporation, Chemistry Division, Argonne National Laboratory [Lemont] (ANL), University Chemical Laboratory, Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Multidisciplinary, 010304 chemical physics, Chemistry, Radical, Ab initio, 010402 general chemistry, 01 natural sciences, 7. Clean energy, Potential energy, Chemical reaction, 0104 chemical sciences, [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, Transition state theory, Ab initio quantum chemistry methods, Chemical physics, 0103 physical sciences, Physical chemistry, Molecule, Reactivity (chemistry), Physics::Chemical Physics
Abstract

A remarkable number of reactions between neutral free radicals and neutral molecules have been shown to remain rapid down to temperatures as low as 20 kelvin. The rate coefficients generally increase as the temperature is lowered. We examined the reasons for this temperature dependence through a combined experimental and theoretical study of the reactions of O(3P) atoms with a range of alkenes. The factors that control the rate coefficients were shown to be rather subtle, but excellent agreement was obtained between the experimental results and microcanonical transition state theory calculations based on ab initio representations of the potential energy surfaces describing the interaction between the reactants.

Published
2007
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14. Synchrotron SAXS Identification of Three Different Size Modes for Soot Nanoparticles in a Diffusion Flame

Author

James Mitchell, S. di Stasio, Michael Wulff, Ludovic Biennier, J.L. LeGarrec, Aerosol and Nanostructures Laboratory [Napoli], Consiglio Nazionale delle Ricerche [Napoli] (CNR), Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Physique des atomes, lasers, molécules et surfaces (PALMS), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), European Synchrotron Radiation Facility (ESRF), FIRB-MIUR projects RBAU01CXNP and RBAU01K749, Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Institut de Physique de Rennes (IPR), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Nucleation, Analytical chemistry, Synchrotron radiation, Combustion, Small angle X-ray scattering, 02 engineering and technology, 010402 general chemistry, 01 natural sciences, Molecular physics, law.invention, Aggregation, Soot, law, Ionization, General Materials Science, Microstructure, Flame soot microtructure, Small-angle X-ray scattering, Chemistry, Diffusion flame, General Chemistry, 021001 nanoscience & nanotechnology, Synchrotron, 0104 chemical sciences, TEM, Nanoparticles, Particle, Particle size, 0210 nano-technology
Abstract

International audience; The high photon flux (1014 photons/s) and high spatial resolution (∼100 μm) of synchrotron radiation available at ID09b/ESRF facility has been exploited in an in situ investigation of the early stages of soot formation in an ethylene-air diffusion flame. SAXS data demonstrate in situ evidence that the size distribution of soot nanoparticles within the flame exhibits three distinct modes at different heights above the burner z's. In particular, at z ∼ 3 mm, small particles (4-6 nm size), called sub-primary particles, are observed to come into existence. The corresponding monomodal distribution is observed to evolve to bimodal one at z > 5 mm, with the sub-primary particle mode being progressively depleted in favor of the growth of a mode corresponding to larger primary particles (10-12 nm size). The sub-primary peak vanishes completely at about z ∼ 20 mm where distribution is again single mode about 12 nm diameter. Porod's plots show that the sub-primaries are born as configurational flat entities similar to discs or lamellae with a small aspect ratio (Porod's exponent about 2), and upon going to higher z's, they approach a spherical form with a smooth surface (Porod's exponent about 4). Moreover, the careful use of Kratky plots has allowed to demonstrate the presence within the flame of very small nuclei, sized about 1.5-2 nm, which have a nucleation burst at about z ∼ 5 mm, whose number concentration progressively decreases at larger z, finally disappearing around z ∼ 15 mm. The relative increase of primary particles (size larger than 12 nm) is found to correspond to the progressive decrease of these very small nuclei (∼2 nm) concentration. At heights larger than 15 mm a strong ionization signal is observed that increases with height. These findings are in agreement with previous experimental works in the literature performed by Transmission Electron Microscopes and Differential Mobility Analyzers as well as with theoretical studies of dimer-dominated stochastic coagulation.

Published
2006
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15. Vibration-rotation pattern in acetylene. II. Introduction of Coriolis coupling in the global model and analysis of emission spectra of hot acetylene around 3 μm

Author

Séverine Robert, Michel Herman, Bertrand R. Rowe, Balakrishna Raghavendra, Badr Amyay, Audrey Moudens, Robert Georges, André Fayt, Jonathan Thiévin, Service de Chimie Quantique et Photophysique, Université libre de Bruxelles (ULB), Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique (BIRA-IASB), Laboratoire de Spectroscopie Moléculaire, Université Catholique de Louvain = Catholic University of Louvain (UCL), Inorganic and Physical Chemistry (IPC), Indian Institute of Science, Astrochimie expérimentale, Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), and Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Analytical chemistry, General Physics and Astronomy, 33.20.Vq, 33.15.Mt, 33.50.Dq, 33.20.Tp, 33.20.Sn, Rotation, 01 natural sciences, Global model, rotational states, chemistry.chemical_compound, symbols.namesake, 0103 physical sciences, Emission spectrum, Physical and Theoretical Chemistry, Coriolis force, 010303 astronomy & astrophysics, [PHYS]Physics [physics], 010304 chemical physics, Fourier transform spectra, Resolution (electron density), State (functional analysis), Doppler effect, Vibration, Acetylene, chemistry, symbols, fluorescence, Atomic physics, organic compounds, vibrational states
Abstract

A high temperature source has been developed and coupled to a high resolution Fourier transform spectrometer to record emission spectra of acetylene around 3 mu m up to 1455 K under Doppler limited resolution (0.015 cm(-1)). The nu(3)-ground state (GS) and nu(2)+nu(4)+nu(5) (Sigma(+)(u) and Delta(u))-GS bands and 76 related hot bands, counting e and f parities separately, are assigned using semiautomatic methods based on a global model to reproduce all related vibration-rotation states. Significantly higher J-values than previously reported are observed for 40 known substates while 37 new e or f vibrational substates, up to about 6000 cm(-1), are identified and characterized by vibration-rotation parameters. The 3 811 new or improved data resulting from the analysis are merged into the database presented by Robert et al. [Mol. Phys. 106, 2581 (2008)], now including 15 562 lines accessing vibrational states up to 8600 cm(-1). A global model, updated as compared to the one in the previous paper, allows all lines in the database to be simultaneously fitted, successfully. The updates are discussed taking into account, in particular, the systematic inclusion of Coriolis interaction. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3200928]

Published
2009
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16. Direct infrared absorption spectroscopy of benzene dimer.

Author

Chandrasekaran V, Biennier L, Arunan E, Talbi D, and Georges R

Subjects
Dimerization, Quantum Theory, Spectrophotometry, Infrared, Benzene chemistry
Abstract

The direct infrared (IR) absorption spectrum of benzene dimer formed in a free-jet expansion was recorded in the 3.3 μm region for the first time. This has led to the observation of the C-H stretching fundamental mode ν(13) (B(1u)), which is both IR and Raman forbidden in the monomer. Moreover, the IR forbidden and Raman allowed ν(7) (E(2g)) mode has been observed as well. These two modes were found to be red-shifted along with the IR allowed ν(20) (E(1u)) mode, as previously reported by Erlekam et al. [Erlekam; Frankowski; Meijer; Gert von Helden J. Chem. Phys.2006, 124, 171101], using ion-dip spectroscopy, contrary to the blue-shift predicted earlier by theoretical studies. The observation of the ν(13) band indicates that the symmetry is reduced in the dimer, confirming the T-shaped structure observed by Erlekam et al. Our experimental results have not provided any direct evidence for the presence of the parallel displaced geometry, the main objective of the present work, as predicted by theoretical calculations.

Published
2011
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17. Low temperature kinetics, crossed beam dynamics and theoretical studies of the reaction S((1)D) + CH4 and low temperature kinetics of S((1)D) + C2H2.

Author

Berteloite C, Le Picard SD, Sims IR, Rosi M, Leonori F, Petrucci R, Balucani N, Wang X, and Casavecchia P

Abstract

The reaction between sulfur atoms in the first electronically excited state, S((1)D), and methane (CH(4)), has been investigated in a complementary fashion in (a) crossed-beam dynamics experiments with mass spectrometric detection and time-of-flight (TOF) analysis at two collision energies (30.4 and 33.6 kJ mol(-1)), (b) low temperature kinetics experiments ranging from 298 K down to 23 K, and (c) electronic structure calculations of stationary points and product energetics on the CH(4)S singlet potential energy surface. The rate coefficients for total loss of S((1)D) are found to be very large (ca. 2 × 10(-10) cm(3) molec(-1) s(-1)) down to very low temperatures indicating that the overall reaction is barrier-less. Similar measurements are also performed for S((1)D) + C(2)H(2), and also for this system the rate coefficients are found to be very large (ca. 3 × 10(-10) cm(3) molec(-1) s(-1)) down to very low temperatures. From laboratory angular and TOF distributions at different product masses for the reaction S((1)D) + CH(4), it is found that the only open reaction channel at the investigated collision energies is that leading to SH + CH(3). The product angular, T(θ), and translational energy, P(E'(T)), distributions in the center-of-mass frame are derived. The reaction dynamics are discussed in terms of two different micromechanisms: a dominant long-lived complex mechanism at small and intermediate impact parameters with a strongly polarized T(θ), and a direct pickup-type (stripping) mechanism occurring at large impact parameters with a strongly forward peaked T(θ). Interpretation of the experimental results on the S((1)D) + CH(4) reaction kinetics and dynamics is assisted by high-level theoretical calculations on the CH(4)S singlet potential energy surface. The dynamics of the SH + CH(3) forming channel are compared with those of the corresponding channel (leading to OH + CH(3)) in the related O((1)D) + CH(4) reaction, previously investigated in crossed-beams in other laboratories at comparable collision energies. The possible astrophysical relevance of S((1)D) reactions with hydrocarbons, especially in the chemistry of cometary comae, is discussed.

Published
2011
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18. Low temperature kinetics: the association of OH radicals with O2.

Author

Tizniti M, Le Picard SD, Canosa A, Sims IR, and Smith IW

Abstract

We report the first measurements of rate constants for the reaction in which OH radicals associate with O(2) to form HO(3). Our recent measurements (Science, 2010, 328, 1258) have shown that the HO-O(2) bond dissociation energy is only (12.3 ± 0.3) kJ mol(-1). Consequently, above ca. 90 K under attainable experimental conditions, the rate of the reverse dissociation of HO(3) becomes comparable to, and then greater than, the rate of the forward association reaction. We have used the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) method to access low temperatures and have explored the kinetics of OH + O(2) + M → HO(3) + M in two series of experiments. At temperatures between 55.9 and 79.2 K, the OH radicals, created by pulsed laser photolysis of H(2)O(2) and observed by laser-induced fluorescence, decayed by pseudo-first-order kinetics to effectively zero concentration at longer times. The third-order rate constants derived from these experiments fit the expression: k(3rd)(o) (T) = (4.2 ± 1.9) × 10(-34) (T/298 K)(-(3.5 ± 0.3)) cm(6) molecule(-2) s(-1). At temperatures between 87.4 and 99.8 K, rate constants for the association reaction were determined allowing for the significant occurrence of the reverse dissociation reaction. The values of the derived rate constants are consistent with those obtained in the lower temperature range, though the errors are larger. The experimental values of k(3rd)(o) (T) are compared with (a) those for other association reactions involving species of similar complexity, and (b) values of k(3rd)(o) (T) estimated according to both the energy transfer (ET) and the radical-complex (RC) mechanisms. We conclude that the RC mechanism probably makes the major contribution to the association of OH + O(2) at the low temperatures of our experiments.

Published
2010
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19. A chemical dynamics, kinetics, and theoretical study on the reaction of the cyano radical (CN; X(2)Sigma+) with phenylacetylene (C6H5CCH; X(1)A1).

Author

Bennett CJ, Morales SB, Le Picard SD, Canosa A, Sims IR, Shih YH, Chang AH, Gu X, Zhang F, and Kaiser RI

Abstract

The chemical reaction dynamics to form o-, m-, and p-cyanophenylacetylene via the neutral-neutral reaction of ground state cyano radicals with phenylacetylene and D(1)-phenylacetylene were investigated in crossed beam experiments; these studies were combined with kinetics measurements of the rate coefficients at temperatures of 123, 200, and 298 K and supplemented by electronic structure calculations. The data suggest that the reaction is initiated by a barrier-less addition of the electrophilic cyano radical to the o-, m-, or p-position of the aromatic ring. The eventually fragmented via atomic hydrogen elimination to form o-, m-, and p-cyanophenylacetylene via tight exit transition states with the hydrogen atom being ejected almost perpendicularly to the molecular plane of the rotating complex. The overall reaction to form o-, m-, and p-cyanophenylacetylene was found to be exoergic by 89 +/- 18 kJ mol(-1) in nice agreement with the calculations. The o-cyanophenylacetylene isomer is of particular relevance as a potential building block to the formation of nitrogen-substituted didehydronaphthalene molecules in analogy to didehydronaphthalene in Titan's aerosol layers--a pathway hitherto neglected by the planetary science modeling community.

Published
2010
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20. The thermodynamics of the elusive HO3 radical.

Author

Le Picard SD, Tizniti M, Canosa A, Sims IR, and Smith IW

Abstract

The role of HO3 as a temporary reservoir of atmospheric OH radicals remains an open question largely because of the considerable uncertainty in the value of the dissociation energy of the HO-O2 bond (D0) or, equivalently, the standard enthalpy of formation of HO3 (Delta(f)H;{\overline{);\circ }}$$). Using a supersonic flow apparatus, we have observed by means of laser-induced fluorescence the decay of OH radicals in the presence of O2 at temperatures between 55.7 and 110.8 kelvin (K). Between 87.4 and 99.8 K, the OH concentration approached a nonzero value at long times, allowing equilibrium constants for the reaction with O2 to be calculated. Using expressions for the equilibrium constant from classical and statistical thermodynamics, and values of partition functions and standard entropies calculated from spectroscopic data, we derived values of D0 = (12.3 +/- 0.3) kilojoules per mole and Delta(f)H;{\overline{);\circ }}$$ (298 K) = (19.3 +/- 0.5) kilojoules per mole. The atmospheric implications of HO3 formation are therefore very slight.

Published
2010
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21. Low temperature rate coefficients for reactions of the butadiynyl radical, C4H, with various hydrocarbons. Part I: reactions with alkanes (CH4, C2H6, C3H8, C4H10).

Author

Berteloite C, Le Picard SD, Balucani N, Canosa A, and Sims IR

Abstract

The kinetics of the reactions of the linear butadiynyl radical, C4H (CCCCH), with methane, ethane, propane and butane have been studied over the temperature range of 39-300 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. The rate coefficients, except for the reaction with methane, show a negative temperature dependence and can be fitted with the following expressions over the temperature range of this study: k(C2H6) = 0.289 x 10(-10) (T/298 K)(-1.23) exp(-24.8 K/T) cm3 molecule(-1) s(-1); k(C3H8) = 1.06 x 10(-10) (T/298 K)(-1.36) exp(-56.9 K/T) cm3 molecule(-1) s(-1); k(C4H10) = 2.93 x 10(-10) (T/298 K)(-1.30) exp(-90.1 K/T) cm3 molecule(-1) s(-1). The rate coefficients for the reaction with methane were measured only at 200 K and 300 K yielding a positive temperature dependence: k(CH4) = 1.63 x 10(-11) exp(-610 K/T) cm3 molecule(-1) s(-1). Possible reaction mechanisms and product channels are discussed in detail for each of these reactions. Potential implications of these results for models of low temperature chemical environments, in particular cold interstellar clouds and planetary atmospheres such as that of Titan, are considered.

Published
2010
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22. Low temperature rate coefficients for reactions of the butadiynyl radical, C4H, with various hydrocarbons. Part II: reactions with alkenes (ethylene, propene, 1-butene), dienes (allene, 1,3-butadiene) and alkynes (acetylene, propyne and 1-butyne).

Author

Berteloite C, Le Picard SD, Balucani N, Canosa A, and Sims IR

Abstract

The kinetics of the reactions of the linear butadiynyl radical, C4H (CCCCH), with a variety of unsaturated hydrocarbons have been studied over the temperature range of 39-300 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme, or reaction kinetics in uniform supersonic flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. The rate coefficients for all the reactions studied are found to all be in excess of 10(-10) cm(3) molecule(-1) s(-1) over the entire temperature range. They can be fitted with the following expressions (valid from 39 K to 300 K, with RMS deviations of the experimental points from the predicted values shown, to which should be added 10% possible systematic error) for reaction of C4H with alkenes: k(C2H4) = (1.95 +/- 0.17) x 10(-10) (T/298 K)(-0.40) exp(9.4 K/T) cm3 molecule(-1) s(-1); k(C3H6) = (3.25 +/- 0.12) x 10(-10) (T/298 K)(-0.84) exp(-48.9 K/T) cm3 molecule(-1) s(-1); k(1-C4H8) = (6.30 +/- 0.35) x 10(-10) (T/298 K)(-0.61) exp(-65.0 K/T) cm3 molecule(-1) s(-1), for reaction of C4H with dienes: k(C3H4) = (3.70 +/- 0.34) x 10(-10) (T/298 K)(-1.18) exp(-91.1 K/T) cm3 molecule(-1) s(-1); k(1,3-C4H6) = (5.37 +/- 0.30) x 10(-10) (T/298 K)(-1.25) exp(-116.8 K/T) cm3 molecule(-1) s(-1), and for reaction of C4H with alkynes: k(C2H2) = (1.82 +/- 0.19) x 10(-10) (T/298 K)(-1.06) exp(-65.9 K/T) cm3 molecule(-1) s(-1); k(C3H4) = (3.20 +/- 0.08) x 10(-10) (T/298 K)(-0.82) exp(-47.5 K/T) cm3 molecule(-1) s(-1); k(1-C4H6) = (3.48 +/- 0.14) x 10(-10) (T/298 K)(-0.65) exp(-58.4 K/T) cm3 molecule(-1) s(-1). Possible reaction mechanisms and product channels are discussed in detail for each of these reactions. Potential implications of these results for models of low temperature chemical environments, in particular cold interstellar clouds and star-forming regions, are considered.

Published
2010
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23. Experimental measurements of low temperature rate coefficients for neutral-neutral reactions of interest for atmospheric chemistry of Titan, Pluto and Triton: reactions of the CN radical.

Author

Morales SB, Le Picard SD, Canosa A, and Sims IR

Abstract

The kinetics of the reactions of cyano radical, CN (X2sigma+) with three hydrocarbons, propane (CH3CH2CH3), propene (CH3CH=CH2) and 1-butyne (CH[triple band]CCH2CH3) have been studied over the temperature range of 23-298 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. These reactions are of interest for the cold atmospheres of Titan, Pluto and Triton, as they might participate in the formation of nitrogen and carbon bearing molecules, including nitriles, that are thought to play an important role in the formation of hazes and biological molecules. All three reactions are rapid with rate coefficients in excess of 10(-10) cm3 molecule(-1) s(-1) at the lowest temperatures of this study and show behaviour characteristic of barrierless reactions. Temperature dependences, different for each reaction, are compared to those used in the most recent photochemical models of Titan's atmosphere.

Published
2010
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24. Direct absorption spectroscopy of water clusters formed in a continuous slit nozzle expansion.

Author

Moudens A, Georges R, Goubet M, Makarewicz J, Lokshtanov SE, and Vigasin AA

Abstract

In this article, we report on a Fourier transform infrared study of absorption bands belonging to small-sized water clusters formed in a continuous slit nozzle expansion of water vapor seeded in argon carrier gas. Clear signatures of free and H-bonded OH vibrations in water aggregates from dimer to pentamer are seen in our spectra. Following an increase in argon backing pressure, the position of the cluster absorption bands varies from those characteristics of isolated water aggregates in the gas phase to those known for clusters trapped in a static argon matrix. These variations can be interpreted in terms of sequential solvation of the water clusters by an increasing number of argon atoms attached to water clusters. Our measured spectra are in good agreement with those obtained previously either for free or Ar coated small-sized water clusters using pulsed slit-jet expansions. Our results are equally in accord with those originating from a variety of tunable laser based techniques using molecular beams or free jets or from the study of water aggregates embedded in rare gas matrices. Distinctions are reported, however, and discussed. Ab initio calculations have made it possible to speculate on the average size of an argon solvation shell around individual clusters as well as on the development of the OH stretch vibrational shifts in mixed (H(2)O)(m)Ar(n) clusters having different compositions and architectures.

Published
2009
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25. Gas-phase infrared spectra of vinyl selenol and vinyl tellurol.

Author

Benidar A, Khater B, Guillemin JC, Gámez JA, and Yáñez M

Subjects
Computer Simulation, Models, Chemical, Quantum Theory, Spectroscopy, Fourier Transform Infrared, Vibration, Coordination Complexes chemistry, Gases chemistry, Organoselenium Compounds chemistry, Vinyl Compounds chemistry
Abstract

The infrared spectra (3500-500 cm(-1)) of gaseous vinyl selenol and vinyl tellurol have been recorded at 0.1 cm(-1) resolution. For the latter the spectra were obtained at room temperature, but for the former a temperature of -40 degrees C was required because of the chemical instability of vinyl selenol at room temperature. To compensate the very weak vapor pressure of vinyl tellurol at room temperature, a long optical path up to 136 m was necessary to record its spectrum. B3LYP density functional theory (DFT) calculations have been performed to assign the different absorption bands. Since an unambiguous assignment of the absorption bands requires a precise knowledge on the relative abundance of the syn and gauche rotamers of these compounds, their relative energies and their anharmonic vibrational frequencies were obtained using a very extended Def2-QZVP basis set. Two rotamers, the syn, which is planar, and a nonplanar gauche, were found to be local minima for both compounds. The gauche rotamer presents two degenerate conformers, which differ by the position of the SeH (TeH) hydrogen atom above or below the molecular plane. Our theoretical results are in good agreement with the main features of the experimental spectra. Fundamental bands and some combination bands of vinyl selenol and vinyl tellurol were assigned and compared with those of vinyl alcohol and vinyl thiol, whose spectra had been reported previously in the literature.

Published
2009
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26. UV absorption cross-sections of a series of dimethylbenzaldehydes.

Author

El Dib G, Chakir A, and Mellouki A

Subjects
Atmosphere, Benzaldehydes radiation effects, Deuterium chemistry, Light, Photolysis, Spectrophotometry, Ultraviolet methods, Temperature, Ultraviolet Rays, Benzaldehydes chemistry
Abstract

The ultraviolet absorption cross-sections of 2,4-, 2,5-, 2,6-, 3,4- and 3,5- dimethylbenzaldehydes are reported in the wavelength range 240-320 nm. The measurements were carried out in the temperature range 318-363 K using two different experimental systems (D 2 lamp-monochromator and D 2 lamp-diode array). The absorption spectra of the five aldehydes have been found to exhibit relatively high absorption cross-sections in the region of the tropospheric interest with maxima around 290 nm. This work provides the first UV cross-section measurements for these aromatic aldehydes. The obtained cross-section values enable us to estimate the tropospheric photolysis lifetimes of these compounds. The results suggest that photolysis could be an important removal process for these species in the troposphere.

Published
2008
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27. Understanding reactivity at very low temperatures: the reactions of oxygen atoms with alkenes.

Author

Sabbah H, Biennier L, Sims IR, Georgievskii Y, Klippenstein SJ, and Smith IW

Abstract

A remarkable number of reactions between neutral free radicals and neutral molecules have been shown to remain rapid down to temperatures as low as 20 kelvin. The rate coefficients generally increase as the temperature is lowered. We examined the reasons for this temperature dependence through a combined experimental and theoretical study of the reactions of O(3P) atoms with a range of alkenes. The factors that control the rate coefficients were shown to be rather subtle, but excellent agreement was obtained between the experimental results and microcanonical transition state theory calculations based on ab initio representations of the potential energy surfaces describing the interaction between the reactants.

Published
2007
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28. An experimental study of the intersystem crossing and reactions of C2(X1Sigmag+) and C2(a3Pi(u)) with O2 and NO at very low temperature (24-300 K).

Author

Páramo A, Canosa A, Le Picard SD, and Sims IR

Abstract

A low-temperature gas-phase kinetics study of the reactions and collisional relaxation processes involving C2(X1Sigma(g)+) and C2(a3Pi(u)) in collision with O2 and NO partners at temperatures from 300 to 24 K is reported. The experiments employed a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus to attain low temperatures. The C2 species were created using pulsed laser photolysis at 193 nm of mixtures containing C2Cl4 diluted in N2, Ar, or He carrier gas. C2(X1Sigma(g)+) molecules were detected via pulsed laser-induced fluorescence in the (D1Sigma(u)+ <-- X1Sigma(g)+) system, and C2(a3Pi(u)) molecules were detected via pulsed laser-induced fluorescence in the (d 3Pi(g) <-- a 3Pi(u)) system. Relaxation of 3C2 by intersystem crossing induced by oxygen was measured at temperatures below 200 K, and it was found that this process remains very efficient in the temperature range 50-200 K. Reactivity of C2(X1Sigma(g)+) with oxygen became very inefficient below room temperature. Using these two observations, it was found to be possible to obtain the C2(X1Sigma(g)+) state alone at low temperatures by addition of a suitable concentration of O2 and then study its reactivity with NO without any interference coming from the possible relaxation of C2(a3Pi(u)) to C2(X1Sigma(g)+) induced by this reagent. The rate coefficient for reaction of C2(X1Sigma(g)+) with NO was found to be essentially constant over the temperature range 36-300 K with an average value of (1.6 +/- 0.1) x 10(-10) cm3 molecule(-1) s(-1). Reactivity of C2(a3Pi(u)) with NO was found to possess a slight negative temperature dependence over the temperature range 50-300 K, which is in very good agreement with data obtained at higher temperatures.

Published
2006
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29. Reaction of anthracene with CH radicals: an experimental study of the kinetics between 58 and 470 K.

Author

Goulay F, Rebrion-Rowe C, Biennier L, Le Picard SD, Canosa A, and Rowe BR

Abstract

The rate coefficient of the reaction of the methylidine radical CH with anthracene has been studied over a wide temperature range (58-470 K) in a dedicated "Cinétique de Réaction en Ecoulement Supersonique Uniforme" (Reaction Kinetics in Uniform Supersonic Flow) apparatus. The reaction exhibits a slight positive temperature dependence, which can be fitted to the expression k(T) = (3.32 +/- 1.00) x 10(-10)(T/298)((0.46+/-0.14)) cm3 molecule(-1) s(-1). Even at the lowest temperature, the reaction remains very fast indicating that the kinetics are probably driven by a capture process.

Published
2006
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30. Properties of synthetic ferrihydrite as an amino acid adsorbent and a promoter of peptide bond formation.

Author

Matrajt G and Blanot D

Subjects
Adsorption, Ferric Compounds, Temperature, Time Factors, Amino Acids chemistry, Ferritins chemistry, Peptides chemical synthesis
Abstract

Ferrihydrite, an iron oxide hydroxide, is found in all kinds of environments, from hydrothermal hot springs to extraterrestrial materials. It has been shown that this material is nanoporous, and because of its high surface area, it has outstanding adsorption properties and in some cases catalysis properties. In this work we studied the adsorption properties of ferrihydrite with respect to amino acids. Samples of pure ferrihydrite were synthesised and exposed to solutions of amino acids including both proteinaceous and non-proteinaceous species. These experiments revealed important characteristics of this mineral as both an adsorbent of amino acids and a promoter of peptide bond formation.

Published
2004
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31. Uniform Supersonic Expansion for FTIR Absorption Spectroscopy: The nu(5) Band of (NO)(2) at 26 K.

Author

Benidar A, Georges R, Le Doucen R, Boissoles J, Hamon S, Canosa A, and Rowe BR

Abstract

A high-resolution Fourier transform interferometer (Bruker IFS 120 HR) was combined with a uniform supersonic expansion produced by means of axisymmetric Laval nozzles. The geometry profile of the nozzle enabled us to work under precise thermodynamic and kinetic conditions. The effect of the cooling rate of different nozzles on cluster nucleation is illustrated. The experimental sensitivity was tested by recording the nu(5) band of (NO)(2) at 26 K. Copyright 2000 Academic Press.

Published
2000
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