A molecular dynamics study of the low temperature structure and dynamics of ethane monolayers physisorbed on the graphite basal plane

The three known low-temperature structures of ethane monolayers physisorbed on the graphite basal plane (hereafter called S1, S2, and S3) have been examined by molecular dynamics calculations with intermolecular and molecule–surface potentials based on atom–atom interactions. The structure of the low density S1 phase is shown to be strongly influenced by the corrugation of the graphite surface. The intermediate density S2 phase is incommensurate with a slightly different structure than found experimentally. By contrast, the structure of the high density S3 phase, in which all of the molecules stand erect, appears to be independent of surface corrugation. The dynamical behavior of the three surface phases has been probed by examining power spectra calculated from the hydrogen atom trajectories. The resulting spectra for the S1 and S3 phases agree reasonably well with experimental inelastic incoherent neutron scattering data but not as well in the case of the S2 phase.