THE CHARACTER OF MELTING FOR SIMPLE MOLECULES DEPOSITED ON GRAPHITE

The microscopic character of melting for quasi-two dimensional N-2 adl ayers on graphite is examined for surface densities 0.2 less than or e qual to rho less than or equal to 1, where the upper limit corresponds to a complete monolayer. A Monte Carlo method, with the multiple hist ogram procedure, is employed to determine various thermodynamic quanti ties. Using the calculated specific heats and selected order parameter s, determined at various surface densities, the mechanism for melting is shown to be vacancy mediated. The somewhat unusual behavior of the melting temperature versus density is shown to be entirely due to the vacancy concentration and their topology. Because this is determined b y the free energy, our analysis should be general. Preliminary results for Xe on graphite supports this claim.