Rotation–translation coupling and the lattice dynamics of RbCN

Abstract

The dispersion of acoustic and optical phonons of rubidium cyanide has been measured at 300 K and near the phase transition from the disordered cubic high-temperature phase to the ordered monoclinic phase. At both temperatures the acoustic branches are affected by rotation–translation coupling in a way similar to the findings in KCN. The data are explained by a model which combines a shell model and rotation–translation coupling. The rotation–translation coupling is described on the basis of the theory of Michel and Naudts. Details of the model are discussed.