  Detailed semi-empirical interaction potential calculations are performed to
determine the potential energy surface experienced by the molecules CO, HCN,
H2O and H2CO, when adsorbed on the basal plane (0001) of graphite at low
temperature. The potential energy surface is used to find the equilibrium site
and configuration of a molecule on the surface and its corresponding adsorption
energy. The diffusion constant associated with molecular surface diffusion is
calculated for each molecule.
