Theoretical Simulations of Grain-Surface Processes

Abstract

Recent advances in theoretical simulations of grain-surface processes are reviewed. Classical molecular dynamics (MD) computer simulations were performed to investigate the whole process of H2 formation on icy mantles of interstellar dust grains within a single model. Amorphous water ice slabs were generated at 10 K and 70 K as a realistic model surface of dust grains, and then two incident H atoms were successively thrown onto the surface to reproduce the H2 formation process via H + H → H2 on the dust surface. The following fundamental processes were studied in detail; 1) the sticking of H atom onto the grain surface, 2) the diffusion of H atom on the surface, 3) the reaction of two H atoms on the surface, 4) the ejection of H2 from the surface. Then, the formation pumping mechanism of H2 and the chemical desorption mechanism of frozen CO molecules in the vicinity of H2 forming sites on dust grains were also studied.