Excitation and ionisation in collisions of negatively charged projectiles with atoms

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Abstract
Semiclassical coupled-states calculations have been carried out for collisions involving structureless positively and negatively charged projectiles to explore the dependence of the excitation and ionisation cross sections on the sign of the projectile charge. Both asymmetric collisions, where the magnitude of the projectile charge, Zp, is much less than the target nuclear charge, ZT, so that the perturbation of the target by the projectile is weak, and symmetric collisions, where mod ZP mod approximately=ZT, have been considered. The Coulomb deflection of muons is found to have an appreciable effect on the K-shell ionisation cross section. For the symmetric collision case, the authors' considered excitation and ionisation of atomic hydrogen targets both by protons and antiprotons and by electrons. For protons and antiprotons the ratios of the coupled-state cross sections to the corresponding first Born cross sections do not show the same relation to the first Born that is exhibited by the copper ionisation results, and are in fact remarkably the same for ZP=-1 as for ZP=+1. These results demonstrate the projectile charge asymmetry of the collision, that is due to the presence of the charge transfer channel for the positive projectiles, but its absence for the negative projectiles. For e-+H collisions coupled-state corrections to the first Born approximation are found to be appreciable, and overall good agreement with experiment is found.