Classical Collisions of Dipoles and the Transport Properties of Polar Molecules

Classical trajectories for the collisions of dipolar molecules have been calculated for many initial conditions by stepwise integration of the equations of motion. The molecules were represented by hard spheres with point dipoles at their centers and the motion was confined to a plane. Molecular parameters representing, very crudely, the interactions of CHF₃, CH₃F, and HCl were used and most of the calculations were carried out for relative velocities equal to the mean relative velocity for each gas at 300°K. The translation–rotation energy exchange and the scattering angle are found to be very sensitive to the initial dipole orientations. The mean scattering angle $\chi$ and translation–rotation energy exchange $\mathrm{\Delta E}$ , averaged over the two dipole orientations, are shown to be insensitive to the difference of the angular velocities and to be determined mainly by the sum of the angular velocities. Many of the qualitative features of the collisions are found to be predicted by the rough‐sphere model. In the second half of the paper the quantitative results are applied to the transport properties of polar gases using the kinetic theory equations of Wang Chang and Uhlenbeck. The effect of energy exchange terms in the viscosity formula is estimated and various methods of calculating transport cross sections for dipolar molecules are compared.