Splittings of the librational ground state of CH3D physisorbed on the surface of graphite

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Abstract
Energy levels within the librational ground state manifold of CH3D in a trigonal field are calculated for a monolayer system physisorbed on the surface of graphite. They are classified into two groups: The upper two levels correspond to the stable tripod orientation with the CD bond pointing upward from the surface, and the lower five levels correspond to those with the CD bond pointing toward the surface. The inelastic neutron scattering cross sections are calculated. The transitions between the two groups are found to be negligible. The spectrum for a powdered sample of graphite (Vulcan III) is well reproduced, and that for a partially oriented sample (Papyex) is predicted with momentum transfer both parallel and perpendicular to the surface. Heat capacity anomalies are calculated and found to be sensitive to the spacing between the two groups of levels.