Pure and Applied Chemistry

Abstract: Pressure dependence of the liquid structure and the Raman noncoincidence effect of liquid methanol is examined with the combination of molecular dynamics (MD) simulations and the intermolecular resonant vibrational interactions determined by the transition dipole coupling (TDC) mechanism (MD/TDC method). It is shown that the observed decrease of the Raman noncoincidence ν_NCE of the CO stretching band with increasing density reported in the literature is quantitatively reproduced by the present calculation. As the density increases, the hydrogen bonds get slightly shorter, but molecules belonging to different hydrogen-bond chains get closer to each other to a greater extent. This anisotropic change in the liquid structure is the reason for the behavior of ν_NCE. It is also shown that the concentration dependence of ν_NCE in the methanol/CCl₄ binary mixtures reported in a previous study, and the pressure dependence of ν_NCE in methanol may be described in a consistent way as a function of the number density of methanol in the liquid systems.