Some Recent Developments in the Molecular Treatment of Atom-Atom Collisions

Abstract

Since a few years, we have been applying (at the C.M.O.A.¹ in Paris and at the L.C.A.O.² in Orsay) Molecular Physics Methods to the study of atom-atom or ion-atom collisions at low and moderate energies (from few eV to few keV). The procedure is somewhat similar to that used in the study of Electronic Spectra of Diatomic Molecules. Indeed, in the velocity range under consideration, electrons move generally much faster than the nuclei which suggests to find approximate electronic wavefunctions for the clamped nuclei problem. These functions, in turn, serve as an expansion basis for expressing the total wavefunction that describes both the electrons and the nuclei of the system. The study of an atom-atom collision problem then requires the resolution of a more or less large set of coupled equations. These equations determine the nuclear wave-functions whose assymptotic behavior yield the scattering amplitudes and consequently the cross sections.