Anisotropic interactions between HD molecules

Abstract

The anisotropic interactions between molecules in the heteronuclear hydrogen solids are discussed with stress on their properties of importance for the orientational and translational lattice dynamics. A specific interaction component for homonuclear species, which originates from crystal-field interactions, is suggested and evaluated, in addition to the well-known similar specific component that originates from the isotropic potential due to the shift of the center of mass respective to the charge distribution center. The energy parameters of both specific interaction components have been accurately evaluated and renormalized to account for zero-point translational vibrations. The dispersion laws of the $J=1$ roton excitation in solid HD and DT have been calculated. The bandwidths of the $J=1$ roton excitation are $1.16\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in HD and $0.59\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in DT.