Laboratory investigations of irradiated acetonitrile-containing ices on an interstellar dust analog

Reflection-absorption infrared spectroscopy is used to study the impact of low-energy electron irradiation of acetonitrile-containing ices, under conditions close to those in the dense star-forming regions in the interstellar medium. Both the incident electron energy and the surface coverage were varied. The experiments reveal that solid acetonitrile is desorbed from its ultrathin solid films with a cross section of the order of 10(-17) cm(2). Evidence is presented for a significantly larger desorption cross section for acetonitrile molecules at the water-ice interface, similar to that previously observed for the benzene-water system.