Rotation of a molecule in a solid is strongly suppressed due to the corrugated potential created by the crystal and is reduced to small librations around quasistable positions with infrequent jumps between them. We study how the interaction with the crystal vibrations influences the rotational relaxation of the molecule. A simple model, in which the molecular rotation is described by a 1hyphen;D Langevin equation, is considered. The analytic expressions for the orientational and angular momentum correlation times are obtained. The Hubbard relation, which was established for dense gases and liquids, is shown to be valid for solids in the intermediatehyphen;tohyphen;high damping regime and to be violated at sufficiently low damping. copy;1994 American Institute of Physics.
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