Classical treatment of electron loss

Abstract

The classical impulse approximation is used to calculate the cross section for electron loss from fast projectile atoms. The total loss cross section is the sum of an inelastic contribution which arises from collisions in which the target system is excited or ionized, and an elastic contribution which arises from collisions in which the state of the target system is unchanged. The inelastic contribution may be attributed to electron-electron scattering and its calculation presents no difficulty. The position with regard to the elastic contribution, which is due to electron scattering in the static field of the target, is different. It is inferred from the uncertainty principle that the application of classical mechanics may here lead to serious error, at least for light target systems. Such error is indeed found to occur. However, a classical description of the scattering is remarkably successful in the case of heavy target systems: for example, the derived total loss cross sections in H-Ar collisions do not differ from the corresponding measured cross sections by more than 25% through the impact energy range, 10 kev to 1000 kev, studied. Calculations are also carried out with the target system replaced by a structureless model. Good agreement is obtained with the results of recent measurements which Gilbody et al. (1968) made in the range 60 to 450 kev on loss from metastable helium atoms passing through molecular hydrogen.