Rotationally and vibrationally inelastic scattering in the rotational IOS approximation. Ultrasimple calculation of total (differential, integral, and transport) cross sections for nonspherical molecules

TLDR: In this article, a simple direct derivation of the rotational infinite order sudden (IOS) approximation in molecular scattering theory is given, and connections between simple scattering amplitude formulas, choice of average partial wave parameter, and magnetic transitions are reviewed.

Abstract: A simple, direct derivation of the rotational infinite order sudden (IOS) approximation in molecular scattering theory is given. Connections between simple scattering amplitude formulas, choice of average partial wave parameter, and magnetic transitions are reviewed. Simple procedures for calculating cross sections for specific transitions are discussed and many older model formulas are given clear derivations. Total (summed over rotation) differential, integral, and transport cross sections, useful in the analysis of many experiments involving nonspherical molecules, are shown to be exceedingly simple: They are just averages over the potential angle of cross sections calculated using simple structureless spherical particle formulas and programs. In the case of vibrationally inelastic scattering, the IOSA, without further approximation, provides a well‐defined way to get fully three dimensional cross sections from calculations no more difficult than collinear calculations. Integral, differential, viscosit...