Thermodynamic state dependence of orientational order and rotational relaxation in carbon tetrachloride.

Molecular dynamics simulations show that orientational correlations in carbon tetrachloride span a wide range of distances within the phases that are ordinarily described as orientationally disordered. They are long ranged in the plastic crystal phase, reach up to several solvation layers in the liquid phase, and only involve contact neighbors within the gas phase. On the contrary, short range arrangements are rather similar, with the sequence face-to-face, edge-to-face, and edge-to-edge describing the most populated relative orientations for increasing distances. In what concerns rotational relaxation, it is shown that none of the available theories is able to describe the relationship between rotational relaxation and angular velocity relaxation times for the three phases studied. This is at variance with experimental results obtained long ago for carbon tetrafluoride, which were in excellent accord with J-diffusion, but is in line with recent experimental results for deuterated methane in gas-phase mixtures.