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Etude de l'adsorption de l'ozone et du cyanoacétylène sur une surface de glace d'eau: un modèle de chimie du milieu interstellaire

Abstract : Adsorption of ozone and cyanoacetylene on amorphous water ice was characterized by FTIR spectrometry between 10 and 180 K. Ozone is adsorbed on dangling OH of the ice surface and a desorption activation energy of 20 kJ/mol was measured by Temperature Programmed Desorption (TPD) coupled with FTIR. This value was confirmed by periodical ab initio calculations. Ozone forms a hydrogen bond with the ice surface. Previously to these periodical calculations, the O3•••H2O complexes were modelized. Cyanoacetylene shows two adsorption states on amorphous ice. The first, between 15 and 45 K, is characterized by a hydrogen bond between dangling OH and nitrogen atom of cyanoacetylene. The second, between 45 and 110 K, implies a hydrogen bond between a dangling O of the ice surface and a hydrogen atom of cyanoacetylene. The activation desorption energy for the second state, measured by TPD, is equal to 39 kJ/mol. A proton donor or acceptor character of the cyanoacetylene with ice was observed. These effects also appear in isolated cyanoacetylene∙∙∙water complexes observed in cryogenic matrix. The relative stabilities were determined from ab initio calculations. The kinetic or thermodynamic nature of the adsorption processes was discussed. A preliminary photochemical study of ozone co-adsorbed on ice surface with cyanoacetylene shows that a reaction occurs. This reaction leads to the formation of H2O2, O2 and a third product supposed to be a ketene.
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Contributor : Fabien Borget <>
Submitted on : Wednesday, March 23, 2005 - 10:58:26 AM
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Fabien Borget. Etude de l'adsorption de l'ozone et du cyanoacétylène sur une surface de glace d'eau: un modèle de chimie du milieu interstellaire. Autre. Université de Provence - Aix-Marseille I, 2000. Français. ⟨tel-00008849⟩

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