Raman spectra of the second order in crystals Part II. Gypsum

Abstract

The earlier work on the Raman effect in gypsum has been briefly reviewed. The results obtained from a detailed study of the Raman effect in gypsum using the mercury resonance radiation as exciter are described. The recorded spectrum consists of 34 Raman lines and bands distributed as follows: 10 lines belong to the lattice spectrum, 14 Raman lines Constitute the spectrum of the S04 ion and ten Raman bands make up the spectrum due to the water of crystallisation. The frequency shifts and widths of most of them have been accurately determined. In addition to these, a few other lines and bands have been recorded. Of the 14 Raman lines belonging to the internal oscillations of the SO₄ ion, nine are comparatively more intense and they constitute the first order spectrum. On the basis of the known crystal structure of gypsum, the appearance of the nine lines as fundamentals has been satisfactorily explained. The five feebler lines have been assigned as octaves and combinations of the fundamental frequencies. They constitute the second order spectrum of the SO₄ ion. The Raman bands of water of crystallisation in gypsum exhibit some of the important features characteristic of the Raman bands of ordinary water and of ice. The similarity in the behaviour of the water bands has been attributed to the fact that the water molecules in gypsuln are concentrated in separate sheets parallel to the cleavage face and are only loosely with other ions. The frequencies corresponding to the various maxima observed in the infra-red absorption spectrum of gypsum have been compared with those observed by the author in the Raman spectrum. A complete bibliography on the Raman effect and infra-red studies in gypsum is also included.