Surface Science Investigations of Physics and Chemistry at Icy Interfaces

This paper will describe recent laboratory studies of relevence to understanding the structure and behaviour of icy grains in a variety of astrophysical environments. We will report on two sets of experimental observations; (1) diffusion of water on silica nanoparticle films, and (2) highly efficient desorption of benzene promoted by electronic excitation of water ice. In (1), we will show evidence for thermally-activated water diffusion at temperatures as low as 18 K using reflection-absorption infrared spectroscopy (RAIRS) to probe the OH stretch of adsorbed water molecules and clusters model silica surfaces. We will also present evidence that the diffusion is barrierless at tempertures above 23 K. For (2), we will demonstrate how mass spectrometric measurements reveal efficient benzene desorption from water ice surfaces irradiated by low (<500 eV) energy electron. We will conclude by considering the impact of these observations on icy grain models.