Laser-induced processes in thin ices

Thrower JD, Zacharias H

Abstract

The application of lasers to studying desorption from thin ice films is discussed, with a focus on systems of relevance to interstellar chemistry. Energetic processing of ices bound to interstellar dust grains is introduced, along with a discussion of the photon sources present in such environments. Appropriate laser systems to promote desorption, as well as probe the desorption products are outlined, along with an introduction to the typical measurements that are performed in the laboratory. The various ways in which the incident photons can drive processes such as desorption is then discussed. Absorption by the underlying substrate can lead to a surface heating which drives a thermal desorption process, or produce a population of hot electrons that can drive desorption and surface chemistry through interactions with the adsorbed layer. In addition, the ice layer itself can absorb in the IR through vibrational excitation and in the VUV-UV-visible wavelength ranges through electronic transitions, leading to a variety of possible desorption scenarios. These are discussed in terms of relevant examples taken from the literature.