Time evolution of average rotation axis directions and mean rotation angles of pressurized liquid methyl iodide by molecular dynamics simulation

Abstract

The rotational motion of liquid methyl iodide has been modelled by molecular dynamics simulations under input parameters optimized from literature values to yield the experimental enthalpy of vaporization and permanent dipole moment of the molecule. First, it is shown that results describing the correlation function of the tumbling motion of the molecules agree reasonably well with some corresponding findings from a spectroscopic Raman study. Second, the rotational motion involving the spinning component around the molecule's symmetry axis was simulated, an effect inaccessible by experiment. Third, and most relevant to the author's interests, a group-theoretical formalism was used that generates the time evolution of the average direction of the average rotation axis as well as the mean rotation angle around it. This approach allowed a more realistic understanding of the effects of density and temperature on molecular rotational motion, as well as a better quantification of the influence of short-time inertial decay, than the common approach of studying orientational correlation data along permanently molecule-fixed axis directions. Fourth, site–site radial distribution functions between neighbouring molecules were simulated, establishing a shielding effect that prevents a carbon atom from approaching any other site by their closest distance.