Debye limit of the stochastic rotation operator

A procedure is proposed for calculating in Debye approximation physical quantities related to steady state random thermal motion. The results are expressed in terms of the stochastic rotation operator. Explicit expressions are derived for this operator and its ensemble average in the case of a rotating molecule which is modelled as a sphere, linear rotator or asymmetric rotator. The relevance of these expressions for certain dielectric and nuclear magnetic relaxation processes is considered.