Abstract
Low-temperature measurements of the infrared absorption of small crystals of NaCl are made in the acoustical-mode frequency region. A large contribution to the absorption coefficient of small crystals is found which is not temperature-dependent and is not due to impurities. This absorption is observed to be more sensitive to the density of the powdered sample than to the crystal size. The fundamental absorption of small crystals of NaCl is also measured. The frequency of the peak absorption is seen to be insensitive to the number of crystals per unit volume. The material at the crystal interface strongly affects the shape of the transmission curve. A Green's-function calculation of the surface-induced infrared absorption is made. The surface is simulated by setting nearest-neighbor force constants between atoms in adjacent (001) planes equal to zero.

This publication has 12 references indexed in Scilit: