Orientational dynamics in methanol: influence of temperature and hydrogen bonding

Abstract

Rotational diffusion has been investigated in methanol by means of molecular dynamics simulations at several temperatures, approaching the supercooled state. Angular velocity autocorrelation functions in the molecule-fixed coordinate frame have been evaluated, and the principal components of the rotational diffusion tensor have been obtained. Rotational dynamics of molecules belonging to different hydrogen-bonded states has also been analyzed. It has been found that out-of-plane rotation is favoured at room temperature. Upon cooling, out-of-plane rotational diffusion coefficients decrease faster than in-plane ones, which become largest in the supercooled state. Nevertheless, differences on the microscopic leading mechanisms of rotational diffusion at low temperatures have been identified. For molecules that establish only one hydrogen bond, out-of-plane dynamics is still the most relevant in the supercooled state. Rotational relaxation has also been studied and the available theoretical models have been tested.