Transport Properties of a Gas of Diatomic Molecules. VI. Classical Trajectory Calculations of the Rotational Relaxation Time of the Ar–N2 System

Abstract

The rotational relaxation time of nitrogen in an excess of argon was computed by a fully classical, numerically exact procedure, starting from an estimated anisotropic potential for the $\mathrm{Ar}–{\mathrm{N}}_2$ system. The method involves integration of the second moment of the rotational inelasticity probability density function $\mathcal{P}{\mathrm{(\Delta \; E}}_{\mathrm{rot}})$ over the impact parameter of the collision and a Boltzmann distribution of translational and rotational energies. Confirmatory results were obtained from an integration of the first moment. Both moments of $\mathcal{P}{\mathrm{(\Delta \; E}}_{\mathrm{rot}})$ were evaluated by the classical trajectory CT) method of a previous paper by Pattengill et al. The CT results, extrapolated to the limit of weak anisotropy, agree well with those of the classical generalized phase shift approximation discussed in the preceding paper (V). The present results for the relaxation time P_τ vary, over the temperature range 200–400°K, from 8 to ${\text{20× 10}}^{\text{−10}}\hspace{0.17em}\mathrm{atm}·\sec$ , corresponding to rotational relaxation Z numbers from 6 to 10.