Model for surface reactions on interstellar grains - a numerical study

A model of the formation of molecules by surface reactions on interstellar grains is described and assessed numerically. The model predicts that for the molecules - other than H2 - likely to be important in the interstellar medium, the formation rates by surface reactions are insensitive to the nature of the surface. The formation rates have magnitudes which are significant when compared with other routes. The model also describes H2 formation in high density clouds and shows it to be parameter dependent. (Auth.)