Cosmic ion induced chemistry in ices

Abstract

Since many years, the Laboratory for Experimental Astrophysics in Catania (Italy) has given a contribution to a number of experiments with the aim to investigate the physico-chemical effects induced by fast ions irradiating astrophysical relevant materials. Here, we review some of the most recent results, namely irradiation of mixtures of solid CO and S-bearing molecules. In the interstellar medium, two or more icy compounds can coexist to form ice mantles on grains in two different forms: either they can be mixed together or form separated layers (ice segregation). Thus experiments have been performed with targets prepared at low T (15–20 K) both by a co-deposition of a mixture of two gas compounds (CO and SO2 or H2S) and with targets prepared by deposition of CO ices on a previously deposited SO2 or H2S layer. Samples have been irradiated with 200 keV protons with the aim of simulating a cosmic ion bombardment of interstellar ices. The results show that new chemical species are formed; in particular, OCS and CS2. The astrophysical relevance of the results is discussed.