Multiphonon absorption in alkali halides: Quantum treatment of Morse potential

Abstract

With a view towards calculating the lattice absorption of solids, as a function of frequency and temperature, at frequencies much higher than that of the maximum lattice frequency, a quantum mechanical calculation is given of the absorption involving vibrational levels of a Morse potential that are not adjacent. The thermal average is then taken, and the nature of the solid simulated by a summation over a Debye spectrum. Results are evaluated numerically in the high-temperature approximation, and compared with experimental results on the temperature dependence of absorption by alkali halides at 10.6 μm.