A mean field calculation of the librational properties of δ phase O2 monolayers on graphite

A mean field approximation is used to calculate the librational properties of δ-phase molecular oxygen monolayers on graphite at temperatures 0≤T≤20 K. The frequencies of the two libron modes are found to occur at 35.07 and 60.28 cm−1. The libron specific heat and the rms orientational fluctuations of the O2 molecules about equilibrium are also determined. It is found that the contribution of zero-point orientational fluctuations to librational behavior is large. The molecules exhibit well defined small angle librational motion at low temperatures and there is no evidence of an orientational order–disorder phase transition prior to melting at 25.6 K.