X-Ray and Heat-Capacity Study of Molecular Oxygen Adsorbed on Graphite

In a comprehensive x-ray scattering and heat-capacity study of ${\mathrm{O}}_2$ physisorbed onto basal planes of graphite, at least four independent solid phases are found, whose characters differ markedly from previous descriptions. The most important change is for the monolayer $\delta$ phase, which is believed to consist of a rectangular lattice with the molecules lying down on the graphite surface. The precise nature of several of the higher coverage phases remains unknown.