Interactions and Photochemistry of Small Molecules on Ice Surfaces: From Atmospheric Chemistry to Astrophysics

Abstract

Ice is ubiquitous in the environment, from solid ice at the planet surface to small particles in the atmosphere. The recently identified reactions which occur on the surface of polar stratospheric clouds (PSCs) in the Antarctic winter show that far from being inert, ice is an important surface for heterogeneous atmospheric reactions [1]. Indeed, the majority of studies performed in the laboratory indicate that the availability of accessible water for reaction and product stabilisation is the key to understanding heterogeneous processes on surfaces ranging from sea-salt to sulfuric acid aerosols. Over the last 10–15 years, a wide range of laboratory methods, broadly divided into those which probe surface reaction kinetics and those which probe surface reaction mechanisms [1,2], have been used to study processes relevant to atmospheric ice chemistry. Surprisingly, there are few examples where both mechanism and kinetics have been directly obtained simultaneously, and much of the original ideas concerning the nature of the ice/gas interactions were made by inference from kinetic trends with temperature and pressure. In the first part of this chapter, the nature of the interaction between atmospherically relevant molecules and ice is described, as seen through the application of infrared spectroscopy to the study of thin films of condensed ice at low temperatures.