Infrared absorption due to H− ions in sodium and potassium halides. II. Impurity induced absorption in the far-infrared region

Measurements and calculations of the impurity induced far-infrared absorption due to H− ions in the sodium and potassium halides are presented. The defect model which was previously determined from theoretical fits to experimental local mode and anharmonic side band data is used to predict the absorption spectrum in the far-infrared region below the reststrahlen frequency. The agreement with the observed absorption spectra is good. It is shown that certain features may be interpreted as Van Hove singularities in the unperturbed density of states of the host crystals and that other peaks in the KBr and KI spectra are due to localized resonances.