Correlation of the rotational and translational motions of methanol molecules in pure liquid methanol and in the presence of Li+ ions

Abstract

Molecular dynamics computer simulations of liquid methanol (MeOH) and an infinitely dilute solution of Li+ ions in MeOH at a temperature of 298.15 K were performed. The time autocorrelation functions of the linear (translational) and angular (rotational) velocities and the rotational-translational cross-correlation functions (CCFs) for methanol molecules calculated in the molecular (moving) coordinates, as well as the corresponding spectral functions were analyzed. For bulk methanol, four nonzero of the nine possible CCFs were identified. A relationship between the positions of the peaks in the spectra of the CCFs studied and the spectra of hindered translations and librations of methanol molecules was revealed. It was demonstrated that the introduction of a lithium ion causes substantial changes in the nonzero CCFs for the first solvation shell of the ion but does not give rise to new rotational-translational correlations. The regularities obtained were interpreted in detail at the microscopic level with consideration given to the formation of hydrogen bonds in the solvent and to the anisotropy of intermolecular interactions.