RAMAN AND INFRA-RED STUDIES OF DEFECTSTheory of F-centre Raman scattering in SrF2

Forces and force-constant changes for the F centre in SrF2 were calculated from a point-ion-model, ground-state wave function. The predicted negative central-force-constant change for NN cations is in essential agreement with the value inferred from measured Raman spectra by Glynn, Hayes and Wiltshire. The predicted force-constant change for NN anions is also negative, in contrast to the large positive value inferred from spectra. However, outward radial displacement of NN cations may produce a large, positive central force-constant change for those third-neighbor anions in line with NN cations. It now appears that the latter effect provides a better explanation for an observed A1 resonance in the Raman spectrum at 310 cm-1 than does a hypothetical positive force-constant change for NN anions