Energy states of CH3D molecules in the phase II structure of solid methane

A high resolution neutron scattering study has been made of a solid solution of CH3D (15 mol %) in CH4 at temperatures down to T=1.5 K in order to obtain information about the energy states of CH3D molecules in the phase II structure, i.e., on sites of O and D2d symmetries. Measurements were made with spectrometers IN5 and IN10 at ILL, Grenoble, in the energy range 0<ε<1.3 meV. ‘‘Free’’ rotation and tunneling transitions were observed for both CH3D and CH4 molecules. The results obtained for the tunneling transitions are used to refine the parameters of a model used previously to correlate neutron scattering and thermodynamic data for partially deuterated methanes in the more complicated phase III structure.