Modeling of interstellar surface processes: What does the surface of grains look like?

Computational modeling is discussed of some interstellar surface processes. The surface of interstellar grains is envisaged as covered by at least several layers of weakly bonded molecular material. Simulated amorphous ice particles were used to model interaction of such surfaces with gas, including sticking of H and D atoms, and adsorption of H 2 . A possibility of microporosity of interstellar ice mantles is discussed.