Earth, Planets Space, Vol. 51 (No. 11), pp. 1215-1222, 1999
1National Astronomical Observatory, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
2Institute for Fundamental Chemistry, 34-4, Takano-Nishihiraki-cho, Sakyo-ku, Kyoto 606-8103, Japan
3Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, U.K.
(Received November 24, 1998; Revised April 23, 1999; Accepted May 7, 1999)
Abstract: Recent advances in a series of studies based on the molecular dynamics (MD) computer simulation that was performed to investigate the whole of H2 formation process on the surface of dust grains throughout within a single model are reviewed. Amorphous water ice slabs were generated at 10 K and 70 K as a model surface of dust grains, and then the first and second incident H atoms were thrown onto the surface. The following fundamental processes of H2 formation via two H atoms' recombination, H + H H2, were studied in detail; 1) the sticking of H atom onto the 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 ice surface. The sticking probability, the mobility, the reaction probability, and the ejection lifetime were selfconsistantly obtained for the above processes. The product energy distribution of H2 molecules formed on icy mantles of dust grains was also studied, and it was found that H2 molecules can be highly vibrationally excited by formation pumping mechanism.