Abstract
On the basis of a microscopic model, the dynamic properties of orientationally disordered crystals with substitutional impurity atoms are investigated. The temperature and concentration dependence of the acoustic phonon frequencies is studied. The anomalous damping of phonons is explained. The resonances of the dynamic response function are studied as a function of frequency. The central peak is obtained as a static phenomenon; its temperature dependence is derived. A theoretical foundation for NMR line shapes and x-ray linewidths is presented, and the relation of these data with the central peak is established.