Selection rules for second order infrared and raman processes. II. Fluorite structure and the interpretation of the second order infrared and Raman spectra of CaF2

Group theoretical symmetry assignments for the phonons and the corresponding selection rules for the two phonon infrared absorption and Raman scattering processes for the calcium fluoride structure are given. The selection rules are reasonably favourable for both second order infrared absorption and second order Raman scattering processes. The second order Raman and infrared spectra are interpreted in terms of phonon pair frequencies at the critical points in the Brillouin zone using a. combination of the theoretical dispersion curves of Ganesan and Srinivasan and the neutron scattering data of Cribier, Farnoux and Jacrot.