Equilibrium conformation and surface motion of hydrocarbon molecules physisorbed on graphit

The equilibrium configurations of methane, ethane, propane, ethylene, benzene, cyclohexane and cyclohexane adsorbed on the basal plane of a graphite crystal have been determined in the additive pairwise approximation with Lennard-Jones potentials and using Steele's method of potential expansion. The normal modes for the motion of the rigid molecules at the graphite surface and the corresponding zero point energies have been studied in the harmonic approximation. The evaluation of the adsorption energies has been improved through a perturbative method using the harmonic functions as zero approximation.