Effect of Fluid Rotational Degrees of Freedom on Brownian Motion: Estimates for Water

Expressions are given for the friction force and velocity autocorrelation function of a hard-spherical Brownian particle with "stick" boundary conditions in a fluid with internal rotational degrees of freedom. The velocity autocorrelation function is found to have a $t^{-\frac{3}{2}}$ tail. Comparison with recent experiments indicates that rotational transport coefficients may be measurable by means of light-scattering experiments on Brownian particles. Preliminary estimates are given for rotational transport coefficients of water.