Structural characteristic of irradiated and unirradiated ices

Abstract

We have studied experimentally the structure of H 2O and H 2O:CO ices, as well as structural changes induced by ion irradiation, using infrared (IR) spectroscopy. In fact, IR band profiles (shape, width and peak position) are sensitive to the structure of ices. Results show that the structure of water ice, formed by vapor deposition onto a given substratum, depends both on the temperature (in the range 10–160 K) at which ice films are formed and on thermal and/or irradiation history. CO molecules can occupy two different sites in a water matrix and give rise to an asymmetric IR absorption band profile. A detailed study of this latter, as a function of thermal and/or irradiation history, gives relevant information on the structure of the ice. Ice mixtures have been prepared both by codeposition of H 2O and CO and by diffusion of CO into a preformed water-ice film. These studies are important to understand physical and chemical characteristics of ices even in astrophysical environments. In this latter case information on the history of molecular ices are obtained comparing observed spectra with those taken in the laboratory.