Rotational Brownian motion in a fluid with internal degrees of freedom

The coefficient of frictional torque acting on a rough hard sphere (Brownian particle) which rotates about a fixed axis in a fluid composed of finite-sized particles with internal rotational degrees of freedom is computed. Inertial effects are included. The long-time limit of the angular-velocity-autocorrelation function is obtained. We find that angular-velocity-autocorrelation function decays as $t^{\frac{-5\mathrm{}}{2}}$, but with a coefficient that is altered from the usual Navier-Stokes result to include contributions from transport processes involving internal rotational degrees of freedom of the fluid.