Radiolysis of astrophysical ices by heavy ion irradiation: destruction cross section measurement
A.L.F. de Barros1, P. Boduch2, A. Domaracka2, H. Rothard2, and E.F. da Silveira3
1Departamento de Disciplinas Básicas e Gerais, CEFET-RJ, Av. Maracanã 229, 20271-110 Rio de Janeiro, RJ, Brazil
2Centre de Recherche sur les Ions, les Matériaux et la Photonique (CEA/CNRS/ ENSICAEN/Université de Caen-Basse Normandie), CIMAP-CIRIL-Ganil, Boulevard Henri Becquerel, BP 5133, F-14070 Caen Cedex 05, France
3Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente 225, 22451-900, Rio de Janeiro, RJ, Brazil
Received April 19, 2012
Many solar system objects, such as planets and their satellites, dust grains in rings, and comets, are known to either be made of ices or to have icy surfaces. These ices are exposed to ionizing radiation including keV, MeV
and GeV ions from solar wind or cosmic rays. Moreover, icy dust grains are present in interstellar space and in particular in dense molecular clouds. Radiation effects include radiolysis (the destruction of molecules leading
to formation of radicals), the formation of new molecules following radiolysis, the desorption or sputtering of atoms or molecules from the surface, compaction of porous ices, and phase changes. This review discusses the application of infrared spectroscopy FTIR to study the evolution of the chemical composition of ices containing the most abundant molecular species found in the solar system and interstellar medium, such as H2O, CO, CO2
and hydrocarbons. We focus on the evolution of chemical composition with ion fluence in order to deduce the
corresponding destruction and formation cross sections. Although initial approach focused on product identification, it became increasingly necessary to work toward a comprehensive understanding of ice chemistry. The abundances of these molecules in different phases of ice mantles provide important clues to the chemical processes in dense interstellar clouds, and therefore it is of importance to accurately measure the quantities such as dissociation and formation cross sections of the infrared features of these molecules. We also are able to obtain the scaling of these cross sections with deposited energy.
PACS: 34.50.–s Scattering of atoms and molecules; PACS: 61.80.–x Physical radiation effects, radiation damage; PACS: 33.20.Ea Infrared spectra; PACS: 82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions.