The form of an internal reorientational correlation function

Abstract

A non-Markovian, non-linearly coupled quantum stochastic dynamics model was used to investigate the reorientational correlation function of the internal motion of a methyl group attached to a large molecule. The values for the parameters used were determined by comparing angular momentum correlation functions calculated from the stochastic model to results of a molecular dynamics simulation. The results show that the correlation function has a rapid short time decay due to inertial effects, followed by a slower, exponential tail. Thus if there is significant inertial motion it is necessary to have at least two order parameters as well as two correlation times, one each for the overall and the internal motion, in order to accurately describe the system. The model can also explain data of Lee and McClung that cannot be explained with a Markovian model.