Single crystal laser Raman spectroscopy

Abstract

The chemical implications of single crystal Raman spectroscopy by means of laser excitation are briefly outlined. Unambiguous assignments are presented for PdCl$^{2-}_4$, PtCl$^{2-}_4$, PtCl$^{2-}_6$. PdCl$^{2-}_6$, GeCl$^{2-}_6$ and TeCl$^{2-}_6$ species. Detailed scattering equations are applied to mercurous chloride. The vibrational spectra of cassiterite, anatase and rutile are discussed in terms of the factor group. Gallium trichloride and aluminium tribromide spectra are discussed from the viewpoint of a perturbed D$_{2h}$ Raman tensor. The complex spectrum of molybdenum trioxide is interpreted in terms of a site-factor group analysis. Problems of birefringence, crystal imperfection, dichroism, the resonance Raman effect, twinning, enantiomorphism, internal reflexion and dependence of relative intensity on physical state are noted. The methods discussed are applied to the first-order spectra of centrosymmetric crystals and rely on the validity of the Raman tensor predictions resulting from factor group analysis.