Volume 531, July 2011
|Number of page(s)||9|
|Section||Atomic, molecular, and nuclear data|
|Published online||06 July 2011|
Cosmic ray impact on astrophysical ices: laboratory studies on heavy ion irradiation of methane
Departamento de Disciplinas Básicas e Gerais, CEFET-RJ, Av. Maracanã 229, 20271-110, Rio de Janeiro, RJ, Brazil
2 Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente 225, 22453-900 Rio de Janeiro, RJ, Brazil
3 Grupo de Física e Astronomia, Instituto Federal do Rio de Janeiro (IFRJ), Rua Lucio Tavares 1045, 26530-060 Nilópolis, RJ, Brazil
4 Centre de Recherche sur les Ions, les Matériaux et la Photonique CIMAP-GANIL (CEA-CNRS-ENSICAEN-UCBN), BP 5133, Boulevard Henri Becquerel, 14070 Caen Cedex 05, France
Received: 28 October 2010
Accepted: 18 April 2011
Laboratory data of CH4 ice radiolysis promoted by fast heavy ions are obtained by infrared spectroscopy (FTIR). CH4 molecules are condensed on a CsI substrate at 15 K, and the ice layer is bombarded by 220 MeV 16O7+ ion beam. The ice thickness is thin enough to be traversed by projectiles at constant velocity close to the equilibrium charge state. The induced CH4 dissociation gives rise to the formation of molecular species CH3, C2H2, C2H4, C2H6, and C3H8. Their formation and dissociation cross sections are determined. C2H6 represent the most abundant daughter molecules. The carbon budget analysis of CH4 and its radiolysis products shows that the column density of carbon atoms contained in the methane destroyed during ion irradiation is 30 − 50% greater than the sum for the column densities of the newly formed species. As an astrophysical implication, the current results allow estimation of chemical reaction rates in ices covering interstellar grains.
Key words: astrochemistry / methods: laboratory / circumstellar matter / ISM: clouds / ISM: molecules
© ESO, 2011
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