Theoretical study of the infrared and Raman line shapes of liquid methanol

Abstract

Using a combined electronic structure and molecular dynamics simulation method, we calculated the infrared and Raman spectra for the OH vibrations in liquid CH₃OH. The vibrational frequencies, transition dipole moments, and transition polarizabilities are obtained from density functional theory calculations and then mapped into an empirical relation to the electric field on the H atom along the OH bond. Vibrational couplings between OH chromophores on different molecules are treated using transition dipole interactions. The simulated infrared and Raman line shapes are in good agreement with experimental observations. We have also shown that the vibrations of non-hydrogen-bonded OH groups contribute significantly to the difference between the IR and Raman line shapes.