Rotational relaxation characteristics of the monoclinic phase of CCl

We present a study of crystalline CCl spanning up to 10 orders of magnitude in time at temperatures ranging from 160 K to 190 K using molecular dynamics simulations. The relaxation process is studied using angular self correlation functions. The results show that each of the four nonequivalent molecules of the monoclinic phase have a particular relaxation time. Two of the molecules relax in an exponential way and the two other molecules have a more complex behavior, especially at the lower temperatures. In all cases, the molecular rotations correspond to quick jumps between equivalent tetrahedral equilibrium positions. Most of these rotations are about the C symmetry axes, however at high temperatures, rotations about the C symmetry axes are observed as well. The waiting time between rotations follows a Poisson distribution. The calculated relaxation times show an Arrhenius behavior with different activation energy for different nonequivalent molecules, in line with recently published findings of nuclear quadrupole resonance experiments. © 2011 American Institute of Physics.