PHASE-BEHAVIOR OF OXYGEN ADSORBED ON GRAPHITE

Molecular dynamics simulations are performed to investigate the physic al adsorption of oxygen on graphite at 15 to 300 K with coverages from 0.192 to 2 monolayers. Below 25 K, the adsorbed molecules have transl ational ordering and are in a solid state. Above 25 K solid clusters a t submonolayer coverages disintegrate to a liquid-like layer without t ranslational ordering. For coverages close to or above monolayer, laye ring transition and some out-of-plane orientations are observed at hig h temperatures. More adsorbed molecules escape into the gas phase at h igher temperatures and the equilibrium vapour pressure can be estimate d by the bulk phase density. A phase diagram is constructed summarizin g these changes and the adsorption isotherms. (C) 1997 Elsevier Scienc e B.V.