Impulse approximation for three-dimensional inelastic atom—diatomic-molecule collisions

Abstract

The impulse approximation of Chew is applied to the calculation of the cross sections for rotational and vibrational excitation of diatomic molecules by collisions with an atom. The assumptions underlying the impulse approximation are discussed and found to be justified for these processes. A closure approximation is used to perform the sums over rotational quantum numbers in the expression for the vibrational-excitation cross section and the resulting expression depends on two factors; an oscillator form factor and the scattering amplitudes for atom-atom scattering. Vibrational-transition probabilities, evaluated for oxygen-carbon monoxide collisions assuming that the oscillator is harmonic and using a rough estimate for the typical atom-atom scattering amplitudes, are in qualitative agreement with experiment. Further refinements and extensions of the model are discussed.