Abstract
The triple differential cross section (TDCS) for electron impact ionization of atoms is proportional to the momentum density of the ejected electron under conditions when the colliding electrons can be considered to be free and the interactions between the incident, scattered and ejected electrons with the residual ion can be neglected. These are the conditions of the plane wave impulse approximation (PWIA). Under such circumstances, the measured “momentum densities” can be used to investigate single electron atomic wave functions and correlate these with the chemical and physical properties of the atoms. For these studies to be meaningful, the data should have a relative precision of 5 to 10%, (see for example the discussion of experimental precision in (e, 2e) collisions by Moore et al.1) To attain this degree of precision at incident electron energies of 1 keV or greater, the typical energies for such experiments, requires data acquisition times of several hours to days with current technologies. An alternative is to decrease the incident energy in order to increase the absolute value of the TDCS. While this is an attractive alternative, it is essential to recognize that as the incident energy is decreased the interactions between the incident, scattered and ejected electrons and the residual ion become relatively more important, until the point is reached where the TDCS is not even approximately proportional to the single electron momentum density.
Published Version
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