Critical temperatures of two-dimensional condensation in the first adlayer of noble gases on the cleavage face of graphite

A set of adsorption isotherms of Ar on the basal face of graphite gives for the critical temperature of two-dimensional condensation in the first adlayer a value of 59±{}1 K, significantly different from that previously accepted. This value, together with those obtained for Kr and Xe, agrees well with the prediction of a virial expansion truncated after the fourth coefficient, suggesting that the liquid phases of the first monolayers of noble gases adsorbed on graphite are not significantly perturbed by the surface structure.