Raman study of molecular aggregation in liquid dimethyl sulfoxide

Parallel I _∥(ν) and perpendicular I _⊥(ν) polarized components of the S=O band in the Raman spectrum of liquid dimethyl sulfoxide (DMSO) were found to consist of at least three lines each. The depolarization ratios of these lines are different. Only the high-frequency line remains in both components after high dilution of DMSO with CCl₄ 10 mol %. All three lines are present in both components even after high dilution of DMSO with nitromethane, with their intensities being changed only slightly. These facts were explained by the occurrence of various molecular aggregates along with individual (monomeric) molecules present in DMSO and its nitromethane solutions. The monomeric molecules are predominant in a highly diluted CCl₄ solution. The polarized components of the S=O band of an aqueous DMSO solution point to the presence of H-aggregated formations of two types. The similarity in the molecular structure of DMSO and acetone makes it possible to assume that there are aggregated formations in liquid acetone as well. The small difference in wavenumbers as well as the overlap of the lines belonging to various aggregated formations may lead to the noncoincidence of the peaks of unresolved I _∥(ν) and I _⊥(ν) components of the C=O band of acetone.