The effects of pressure and temperature on vibrational dephasing in a simulation of liquid CH₃CN

Abstract

A principal cause of vibrational dephasing in molecules in liquids is the interaction of the components of intermolecular forces along normal modes with cubic anharmonicities. The amplitude and dynamics of the fluctuations in the forces along the two normal modes of CH₃CN were compared for simulations of the liquid state at different densities and at different temperatures. In all cases the modes were homogeneously broadened. There are considerable differences in the amplitude and dynamics of the fluctuations in the forces along the two normal modes which can be attributed to the relative importance of the repulsive and electrostatic parts of the intermolecular forces. Comparisons are made with the predictions of isolated binary collision and density fluctuation theories for vibrational dephasing, as well as with published experimental data.