Liquid Structures and the Infrared and Isotropic/Anisotropic Raman Noncoincidence in Liquid Methanol, a Methanol−LiCl Solution, and a Solvated Electron in Methanol: Molecular Dynamics and ab Initio Molecular Orbital Studies

Abstract

The relationship between the liquid structures, vibrational interactions, and the wavenumber differences among the infrared (IR), isotropic Raman, and anisotropic Raman components of vibrational bands (the noncoincidence effect) is analyzed theoretically for the OH stretching bands of neat liquid methanol and a methanol−LiCl solution. The analysis is also carried out for the CO stretching band of neat liquid methanol for comparison. The IR and Raman spectra are calculated on the basis of the transition dipole coupling (TDC) mechanism and the liquid structures derived from molecular dynamics (MD) simulations (the MD/TDC method). It is shown that the signs and magnitudes of the noncoincidence effect observed for the OH and CO stretching bands of liquid methanol, which are significantly different between these two bands, are well reproduced by the calculations based on the same set of liquid structures and the same mechanism of vibrational interactions. The analysis of the origin of the noncoincidence effect...