Structural features of liquid DMSO from temperature-dependent Raman spectroscopy and theoretical calculations

Dimethyl sulfoxide (DMSO) plays an important role in chemistry, biology and industry. The S=O stretching vibration serves as a sensitive probe of its structure under different chemical environments. However, spectral assignment for the S=O stretching vibration of liquid DMSO remains unclear due to the interference of CH3 antisymmetric rocking and different aggregates, leading to the confusion in explaining the microstructures of liquid DMSO. Here, the S=O stretching spectra in pure DMSO and in extremely diluted CCl4 solution were investigated with temperaturedependent Raman spectroscopy. It is shown that CH3 antisymmetric rocking does not significantly interfere with the S=O band profile due to its low Raman intensity. Three decomposed peaks at 1027, 1042 and 1055 cm−1 in liquid DMSO show obviously different intensity variety upon the temperature increasing. Combined with quantum chemistry calculation on (DMSO)n (n=1–4) clusters, Raman spectra in the S=O stretching region were assigned and the simultaneous presence of the monomer, dimer and trimmer in liquid DMSO were concluded. These results contribute to a more detailed molecular understanding of the structure of DMSO in the liquid state.