Lattice gas transition of xenon on a fullerite surface*

We study a lattice-gas transition of xenon atoms on a honeycomb geometry. It is found from experiments and Monte Carlo simulations that this configuration occurs for xenon adsorbed on a substrate consisting on an array of C60 molecules on Ag(111). At very low coverage the atoms occupy strong-binding 3-fold hollow sites between C60 molecules. In this way, they form a commensurate lattice with nearest neighbor distance 0.58 nm. Using a Lennard Jones model for the Xe-Xe potential, the nearest neighbor interaction strength is U=96.7 K. Using the Ising model we estimate the transition critical temperature to be Tc = 36K. We compare with our results from Monte Carlo simulations based on more realistic interactions.