Molecular Collisions. XVI. Comparison of GPS with Classical Trajectory Calculations of Rotational Inelasticity for the Ar–N2 System

Abstract

The classical limit of the ``infinite order'' generalized phase shift (GPS) treatment of rotationally inelastic atom‐molecule collisions was put into computationally feasible form in Paper XV of this series. It is now applied to a model problem intended to approximate thermal scattering of the Ar–N<sub>2</sub> system (collisional energy of $\frac{3}{2}\mathrm{kT}$ at 300°K), at the same time comparing its predictions with exact classical trajectory (CT) results. This comparison indicates that the present version of the GPS method over‐estimates the rotational excitation and underestimates the de‐excitation, while maintaining the total inelasticity at approximately the correct (CT) value. An approximate ``quantization'' of the classical results leads to an estimate of the quantal cross sections corresponding to changes by ±2, ±4, and ±6 from an initial rotor quantum state $\overline{l}\text{=10.}$ It is found that most of the total inelastic crosssection (of some 32 Ų) arises from the first‐order‐allowed transitions $\text{(Δ l=± 2)}$ .