Studies on the raman spectra of crystals (PHY)

Abstract

The Raman spectra of crystals have formed a very fruitful topic of study in the past and such studies, particularly on single crystals in specific orientations, have contributed in a large measure to a better understanding of the nature of crystalline forces and the influence of local symmetry on the vibrations of polyatomic ions and molecules in crystals. However, due to the anisotropic nature of the crystalline field and/or due to the large number of atoms or molecules in a unit cell, a rigorous mathematical treatment of the vibration spectra of crystals except in very simple cases like the alkali halides is not feasible. But a comparative study of the Raman spectra of related compounds can help us in no small measure in correlating and deriving empirical relations on the influence of the cation, the water of crystallisation etc. on the vibrations of groups such as SO₄ and form the basis for future theoretical progress. In carrying out such a detailed and complete study of the spectra of single crystals, the use of the resonance radiation of mercury has already played a notable part. However, the potentialities of the method offer still a large scope for further use. More detailed investigations on the Raman spectra of single crystals—the method has the added advantage of enabling us to record in a satisfactory manner the complete lattice spectrum. The present investigation has fully justified such an expectation. The thesis embodies the results obtained by the author on some aspects of the spectra of crystals. It has been divided into two parts: The first part deals with the spectra of crystalline sulphates while the second part deals with the polarisation character of the Raman lines of cubic crystals.