Asymptotic cross sections for composite projectile reactions

Abstract

The First Born Approximation has been used to compute excitation and ionization cross sections for ion-atom collisions involving two electrons at high energies. The projectile is treated semi-classically following a straight line path and the target is assumed to be at rest. As a result of their interaction, the ion is excited from Is-2s. The atom may be either elastically scattered, excited, or ionized from its ground state. In order to perform the First Born Approximation exactly, these states must be summed over. This is accomplished with the aid of a FBBS code which determines the cross section. After the interaction potential was calculated and inserted into the code, the code was run with both exponential and gaussian basis functions, which were set with a various number of basis states. The resulting cross sections are then compared with calculations done in 1978 by Bell and Kingston (BK) and in 1993 by Reading, Hall, and Ford (FJ-IF). BK and RBF used quite different methods and yet arrived at the same results. Thus, by comparing our calculations with these separate approaches, we can determine their accuracy. Furthermore, several suggestions are presented in an attempt to explain the results of these collisions along with the nature of the particles involved. The focus of this study is a H atom incident upon a He+. It has also been applied to collisions involving H and Li ' in the place of He' in the hopes of contributing more insight to the results.