Raman Spectroscopy of the Condensed Phase

This article discusses the general factors that influence the appearance of Raman spectra of materials in the condensed phase. The same material, when presented in different physical forms, can have significantly different Raman spectra. This must be taken into account when interpreting condensed phase spectra. After considering the main differences between the spectra of gases and liquids or solids, some effects peculiar to the solid state are discussed in detail. The influence of site and factor group splitting and phonon dispersion is described, as are the practical consequences of polymorphism. The effects of crystal and particle size, lattice defects, and the presence of amorphous domains are discussed, as is the influence of molecular orientation in crystals or drawn polymers. Finally, some artefacts that are prone to occur with condensed phase samples (self-absorption of radiation, fluorescence, and degradation) are mentioned along with ways to minimise their impact. Keywords: Raman; condensed phase; crystal; powder; particle size; liquid; polymorphism; rutile; anatase