Dynamics of xenon, krypton, and methane monolayers in registry with graphite.

The self-consistent phonon (SCP) theory is used to study the dynamics of monolayers of xenon, krypton, and methane adsorbed on graphite. Only the ~3Xv 3 sohd phase is considered. It is shown that the phonon energies of the Xe monolayers are very similar to those of their Soating counterparts, while the interaction of the Kr and CH4 monolayers vnth the graphite signNcantly a8ects the phonon dispersion curves. The gap in the phonon dispersion curves at the center of the Brillouin zone is computed as a function of temperature. At a critical temperature, the gap goes spontaneously to zero and a transition from a locked-in commensurate phase to a floating phase takes place. This transition appears to describe the commensurate to Boating transition in CH&