ISSN:
1434-6079
Keywords:
34.80D
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract The experimental and theoretical situations for direct single ionization by electron impact are reviewed with special emphasis on triple differential cross sections for impact energies between several hundred eV and threshold. These cross sections can now be determined in absolute units, thus providing a powerful test of calculations. Only the target atoms helium and atomic hydrogen are considered, with quite simple wave functions, in order to focus attention on the correct description of the collision mechanism and to investigate the ranges of validity of various theoretical models. For the higher incident energies, processes with asymmetric energy partitioning and small momentum transfer are emphasized. For a long time these processes (which represent the predominant majority of all ionizing collisions) could not be calculated satisfactorily. Substantial progress in the theoretical treatment of the problem now allows the reproduction of the correct intensities and peak positions in the angular correlations of the outgoing electrons. It is now clear that double collisions, at least, have to be taken into account to describe the dynamics of these collisions. At lower energies both escaping electrons move rather slowly in the field of the ion core and exchange effects can no longer be neglected. Therefore, the theoretical situation is still rather involved. Close to threshold, recent triple differential cross section measurements permit a partial wave analysis, which should challenge theorists to explain these data by ab-initio calculations. The last chapter of this report deals with the progress in the determination of reliable absolute double differential cross sections.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01384654
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