Experimental and Theoretical Momentum Transfer Dependence of the He (E, 2e) Cross Section


The relative triple differential cross section for the electron impact ionization of helium has been measured and calculated for an incident energy of 488 eV. This is sufficiently highly asymmetric geometry that exchange processes may be neglected and the slow and fast outgoing electrons identified as ejected and scattered electrons, respectively. For two fixed ejected electron directions ±90°, and ejected electron energy 34.5 eV, coplanar (e, 2e) measurements have been made for a range of scattering angles between ±30°, corresponding to a momentum transfer range 0.38 → 3 au. The data are presented directly as scattered electron angular distributions and in the manipulated form of their sum, difference and the ratio difference / sum. These are compared to four types of theoretical calculations. Excellent agreement is found between experiment and a calculation that includes significant post collision interaction effects. All four calculations predict an almost identical oscillatory feature in the difference and ratio of the ±90° cross sections, which is consistent with the experimental data and is due to the fact that the cross section passes through zero close to, but not exactly at, 0° scattering.




National Science Foundation (U.S.)

Keywords and Phrases

Atomic and Molecular Interactions; Atomic and Molecular Physics; Atomic Excitation and Ionization; Chemical Reactions

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Document Type

Article - Journal

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© 2005 Institute of Physics - IOP Publishing, All rights reserved.

Publication Date

01 May 2005