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STRUCTURE ET DYNAMIQUE DE FILMS DE GLACE SUPPORTÉS. INFLUENCE DE L'ADSORPTION DE HCl, IMPLICATIONS POUR L'ENVIRONNEMENT

Abstract : Since the discovery that heterogeneous gas/ice reactions are involved in the ozone hole depletion a lot of laboratory studies concerning the adsorption of HCl on ice have been done. In this work, the role of HCl adsorption on the structure and dynamics of supported thin ice films is examined. The water monolayer structure is studied by dynamical LEED analysis on MgO single crystal and by neutron diffraction on uniform powders. Atomic positions of the water molecules in the p(3x2) monolayer unit cell are determined. The best agreement between experiment data and theoretical calculations is obtained with a structure in which water molecules are adsorbed out of Mg sites. Structure and dynamics of thicker ice films supported on MgO powders are determined by neutron diffraction and Quasi-Elastic Neutron Scattering. The p(3x2) monolayer coexists with a bulk phase (ice Ih at low temperature, liquid water at 273K). The substrate induces a growth anisotropy of ice crystallites. QENS associated with Molecular Dynamics calculations shows that a quasi-liquid layer appears at the ice surface at 265K. Then, HCl/ice interaction is analysed. HCl destroys in an irreversible way the p(3x2) overlayer structure. The dynamics and the structure of thicker ice films are modified depending on temperature and HCl coverage. A liquid-like film appears at 250K for 0.3 and 0.6 ML of HCl. The mobility decreases at 1 ML, and the film becomes entirely amorphous. Then, we observe at 220K by neutron diffraction the coexistence of hexagonal ice and chlorine dihydrate. Implications for the atmospheric chemistry are discussed. Finally, preliminar studies concerning water adsorption on BaF2(111) are presented. It is shown that barium fluoride is a good single crystal substrate for epitaxial growth of ice thick films.
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https://tel.archives-ouvertes.fr/tel-00003590
Contributor : Benjamin Demirdjian <>
Submitted on : Friday, October 17, 2003 - 3:30:17 PM
Last modification on : Wednesday, August 29, 2018 - 11:40:03 AM
Long-term archiving on: : Wednesday, September 12, 2012 - 11:00:31 AM

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Benjamin Demirdjian. STRUCTURE ET DYNAMIQUE DE FILMS DE GLACE SUPPORTÉS. INFLUENCE DE L'ADSORPTION DE HCl, IMPLICATIONS POUR L'ENVIRONNEMENT. Physique [physics]. Université de la Méditerranée - Aix-Marseille II, 2000. Français. ⟨tel-00003590⟩

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