Spectral narrowing and rotational diffusion of molecular impurities in a deformable lattice

Orientational dynamics of a single diatomic molecular impurity in a deformable lattice is investigated using the Mori technique, and results are compared to the rigid-lattice case studied by de Raedt and Michel. The rotation-translation coupling, in addition to modifying the single-site cubic potential, suppresses librational motion, enhances diffusive motion, and narrows the width of the diffuse central peak.