Theoretical Studies of the Influence of an Intermolecular Force and an Electric Field on the Methanol Raman Spectrum

The application of surface-enhanced Raman scattering (SERS) to detect methanol dissolved in transformer oil is one of the most promising online monitoring techniques for evaluating the transformer aging process. In this work, a microscopic cluster of methanol molecules was obtained by combining experiments and methanol molecular simulations, and the vibrational assignments of methanol Raman peaks were determined. A methanol–Ag19 complex was constructed, and the effect of an applied electric field on the charge transfer effect of the complex was analyzed. Applying an electric field will cause the relative position of methanol molecules in the complex to rotate, thereby changing the amount of charge transfer and the polarizability and resulting in charge redistribution and a Raman intensity change. Specifying the electric field strength can enhance or suppress the intensity of the Raman peak caused by the C–O stretching vibration in methanol molecules. Our research strengthens the understanding of the methanol microstructure and the charge transfer effect of an applied electric field on a SERS of a methanol molecule. This is of great importance for monitoring transformer aging with SERS.