Theoretical Interpretation of the Second-Order Raman Spectra of the Alkali Fluoride Crystals

Abstract

In two recent papers we have presented theoretical calculations of the second-order Raman spectra of CsF and NaF. In the case of the latter salt, the agreement with experimental measurements is extremely good. In the case of the former salt, no experimental data are available with which comparison can be made. The object of the present paper is to present systematic calculations of the second-order Raman spectra of the sequence of salts, NaF, KF, RbF, and CsF, so that we may investigate the effects of the different vibrational spectra of these crystals on the computed second-order spectra. In all four cases, we have used two alternative models for the polarizability tensor. These are designed to reduce the eight disposable parameters obtained when one uses a polarizability tensor which is assumed to depend only on the configuration of nearest-neighbor ions to a total of three. For the earlier calculation on NaF, we found that there was no marked difference between the results obtained from the two models, whereas in the case of CsF there was a drastic difference between the two sets of results. The object of the present calculations is to observe the manner in which this difference develops as one proceeds through the fluoride sequence.

Work performed in part under the auspices of the U. S. Atomic Energy Commission.