Raman spectra of the second order in crystals

Abstract

The importance of the study of the second order Raman spectra in crystals for getting a deeper insight into dynamical and optical properties of crystals has been pointed out. The previous work on the Raman effect in calcite has been briefly reviewed. Using the 2536.5 A.U. mercury resonance radiation, the first and second order Raman spectra of calcite have been photographed. As has already been reported the first order spectrum consists of five lines. The frequency shifts and widths of these have been accurately measured. The second order spectrum exhibits a series of eleven lines of varying intensity and width. The frequency shifts of these lines are 221, 864, 1065, 1360, 1583, 1750,2147,2172.5,2220,2310 and 2500 cm -1 . Some of these appear also in the infra-red absorption spectrum of calcite with very nearly the same freequncies. On the basis of the group theoretical analysis given by Bhagavantam, the observed second order Raman lines have been assigned as some of the octaves and allowed combinations of the fundamental frequencies of vibration of the calcite lattice. The existence of Brillouin components along with the unmodified radiation in the light scattered by the crystal of calcite has been demonstrated in a very simple way. A complete bibliography on the Raman effect and infra-red studies in calcite is also included.