Isotope-Induced Far-Infrared Absorption in NaCl and KCl Crystals

Abstract

Band-mode absorption induced by natural isotopes in NaCl and KCl has been measured at 1.8 K in the region of the energy of the acoustic phonon. Absorption peaks, which arise from van Hove singularities, have been observed at 116.8, 122.6 and 145 cm⁻¹ in NaCl, and at 108.2 and 117.0 cm⁻¹ in KCl. The observed absorption spectra are compared with calculated absorption constants which are computed by the theory of Klein and Macdonald with the aid of available data of the shell model of the crystals. Good agreements have been found.