A kinetic theory calculation of the orientational correlation time of a rotorlike molecule in a dense fluid of spheres

The collective and single-particle orientational correlation times are calculated using Boltzmann–Enskog kinetic theory for N rotorlike molecules in a bath of spheres. By assuming that the rotors and bath are hard convex bodies, the collision integrals can be reduced exactly to one- and two-dimensional integrals, which are then readily amenable to numerical quadrature. The calculated correlation times depend on density and temperature in the same way as do the rough hard sphere results. However, the particle shape anisotropy plays the role of the roughness parameters. Comparison of the collective and single-particle orientational correlation times with experiment (including molecular dynamics) indicates that the kinetic theory consistently neglects part of the frictional drag. In all cases studied, the calculated times were a factor of 2 to 4 below the experimental values.