Self-association of dimethyl sulphoxide and its dipolar interactions with water: Raman spectral studies

Raman spectra of solutions of dimethyl sulphoxide (DMSO) in carbon tetrachloride (CCl4) and water are reported for both parallel and perpendicular polarizations in the S=O stretching region. The various bands obtained were subjected to Gaussian band fittings. It was observed that the bands for solutions in CCl4 may be fitted satisfactorily by considering four components and those for solutions in water may be fitted by considering five components. It is inferred that the band at ca 1070 cm-1 observed in the spectra of DMSO in CCl4 belongs to the S=O stretching mode of free DMSO, whereas the two bands observed at ca 1058 cm-1 and ca 1040 cm-1 belong to out-of-phase and in-phase S=O stretchings of the cyclic dimer. The low-frequency band at ca 1025 cm-1 is assigned to linear dimer/higher polymers. Aqueous solutions of DMSO show an additional band at ca 1010 cm-1 due to DMSO hydrogen-bonded with water