Raman Noncoincidence Effect and Intermolecular Interactions in Liquid Dimethyl Sulfoxide: Simulations Based on the Transition Dipole Coupling Mechanism and Liquid Structures Derived by Monte Carlo Method

Model calculations are performed on the Raman noncoincidence effect (frequency difference between the isotropic and anisotropic components) observed in the region of the S=O stretching band of liquid dimethyl sulfoxide (DMSO). Liquid structures are obtained by Monte Carlo simulations, by using potential functions without specific interactions involving the hydrogen atoms of the methyl groups. Intermolecular coupling between the S=O stretches is evaluated by the transition dipole coupling mechanism. The magnitude and the direction of the transition dipole are calculated by ab initio molecular orbital calculations at the second-order Møller–Plesset perturbation level with a basis set extended from 6-31G(2d,p). The calculated sign and magnitude of the Raman noncoincidence are in reasonable agreement with the observed, indicating that the observed large Raman noncoincidence can be mostly explained by the liquid structures obtained without specific interactions involving the hydrogen atoms of the methyl groups. The pair distribution function of liquid DMSO is also calculated to the second order in the orientation correlation of molecules. The origin of the Raman noncoincidence effect is discussed by comparing the cases of liquid DMSO, acetone, and methanol.