The diffusion of H atom on an amorphous surface was investigated, at 10 and 70K, by using classical and quantum approaches. The model amorphous slab was prepared by using classical molecular dynamics simulations, with 2-dimensional periodic boundary conditions and 1000 water molecules in a unit cell. Sticking and diffusion processes were studied for a H atom thrown onto the surface. In the sticking case, the incident H atom initially diffused for 1 to 3ps and then became trapped at one of the stable sites on the amorphous surface. In order to estimate the quantum-mechanical diffusion constant, a new method was developed by using the differential diffusion constant. Rate calculations were performed for a H atom diffusing from one trapping site to another on the amorphous ice. The numerical value was compared with the hopping-rate constant for classical thermal diffusion and a large quantum effect was found.

Quantum Mechanical Treatment for the Diffusion Process of a Hydrogen Atom on the Amorphous Water Ice Surface. J.Takahashi, M.Nagaoka, K.Masuda: International Journal of Quantum Chemistry, 1998, 70[2], 379-85