SPECTRAL SIGNATURE OF LOW-TEMPERATURE HOPPING BETWEEN 2 IMPURITY-INDUCED ELASTIC CONFIGURATIONS

We demonstrate that the jump-rotational-diffusion model originally dev eloped in the context of quasielastic neutron scattering from high tem perature liquids can describe the two-state behavior observed in the l ow temperature dynamics of some molecular and point defects in crystal s. The unusual temperature dependences of the IR spectra of both diato mic chalcogen hydrides in alkali halides and KI:Ag+ can be explained i n terms of two elastic configurations between which the impurities jum p with temperature-dependent dwell times.