We have demonstrated that no linearly coupled, Gaussian stochastic process can reproduce the angular momentum correlation functions we have derived from a molecular dynamics simulation of methyl group in water. Consepquently, a classical, nonlinearly coupled, generalized Fokker- Planck equation was develped for rotational relaxation. The resultant angular mementum correlation functions are in excellent agreement with the simulations.The equations contain several unique features, including multiplicative (rather than additive) noise, a diffusion ~constant~ that depends on the rotaional motion, and the abnormal diffusion term. In the limit of white noise, these equations reduce to the standard linearly coupled equations. With colored noise, however, the linearly and nonlinearly coupled equations are distict and the unique features of the nonlinearly coupled equations drive the dynamic in a fundamentally different way.Development is continueing the extend these results to other systems and applications.
