The Differential Cross Section of Low Energy Electron-Atom Collisions

Abstract

This chapter focuses on experimental work on the differential cross section of electron–atom collisions at low energies, which here means the region of pure elastic scattering limited by the first inelastic threshold. This region differs from the medium and high energy range both as far as experiment and theory are concerned. Because electrons are not scattered inelastically, discrimination against other channels is unnecessary and experimental work can be carried out with quite simple apparatus. The cross section is not strongly forward directed as it is at higher energies. Hence, angular resolution and the capacity of detection at small scattering angles are not so necessary, but the apparatus has to be capable of a large angular range. Theoretical work is, of course, also much less complicated in the region of pure elastic scattering. Basic aspects such as the influence of exchange and target polarization can be studied here most simply. For the same reason, the preferred targets are the rare gases and the alkali metals, which also lend themselves most easily to experimental research. The chapter is concerned only with recent progress made in the study of these targets. The emphasis is on some basic experimental effects found to be responsible for the disagreement, apparent some years ago, between theory and experiment, on checks, which can be made on the data determined experimentally, and on some simple theoretical considerations, which may be of use for the experimentalist.