Decomposition of the CO stretching vibration band of laboratory H2O-CO ices irradiated by heavy ions

Abstract

Abstract H2O and CO molecules are the main constituents of the interstellar dust grain ice mantles. Infrared spectra of the ices in line of sights of young stellar objects and background stars have shown that the CO stretching vibration band can be decomposed into three main components: 2143, 2139 and 2136 cm−1, assigned to CO in different environment sites. The relative strengths between the components have been associated to an evolutionary track of the interstellar molecular clouds. H2O:CO (3:2) and (10:1) ices samples were irradiated by 0.79 MeV/u 58Ni13 + ions to simulate the effects produced by heavy ion cosmic rays in typical interstellar ices mixtures. The CO stretching vibration band is decomposed into six Gaussians functions (2150, 2144, 2141, 2138, 2136 and 2133 cm−1) and their integrated absorbances were measured as a function of fluence. The results have shown that, at the final fluence, the component 2138 cm−1 is the main component of the CO stretching vibration band. The component 2150 cm−1 disappears at the beginning of irradiation. Based on the present and previous results, a time scale for the components in the interstellar ices is proposed. For H2O:CO ice in the ISM it is predicted that, after 1 Myrs, the main components of the CO stretching vibration band are the 2138 cm−1 and 2141 cm−1, due to the CO monomers and dimers, respectively.