Far infrared emission of alkali halide crystals and melts

Abstract

The far infrared emission spectra of several alkali halides (RbCl, NaCl, NaBr, Nal, KBr, KI, CsF, Csl) below and above their melting points are presented and discussed. The instrumentation, accessory high-temperature apparatus, Fourier transform techniques and experimental procedure are outlined. The method involves measuring the spectral emission from a heated sample, where the sample itself is the infrared source. Examples using the classical dispersion model are given to calculate the temperature dependent emissivity spectra. The liquid emission spectra are simulated by increasing the values of the damping constant, which characterize a highly anharmonic system. The phonon lifetimes of the molten salts are estimated to be of the order 10- 12 to 10 -13 s. The approach to the dynamics of the liquid state is from that of a very anharmonic solid.