Investigating many-electron exchange effects in electron–heavy-atom scattering

Abstract

In a recent publication we presented measurements and distorted-wave Born approximation ͑DWBA͒ calculations for spin asymmetries resulting from the scattering of 148 eV spin-polarized electrons from groundstate xenon atoms. While achieving reasonably good agreement between theory and experiment by accounting for many-body exchange effects through a local exchange potential, sizable discrepancies remained in some cases. It was proposed that a more sophisticated treatment of exchange might be the key to obtaining better agreement. Here we present high-precision experimental results at a lower projectile-electron energy of 112 eV. Due to improvements made to our spectrometer, these data are of significantly-improved statistical accuracy over those obtained previously. They are compared to DWBA calculations, within whose framework electron exchange is treated in three different ways. In the first, only exchange between the projectile electron and ejected target electron is considered and that between the continuum-and bound-electrons is ignored. In the second, exchange between the continuum-and bound-electrons is treated through a local approximation. Finally, exchange is included through a Hartree-Fock ͑HF͒ calculation of wave functions for both bound-and continuum-electrons. While this more sophisticated treatment of exchange narrows the gap between experiment and theory, the results suggest improvements in other aspects of the problem may be warranted.

Near-threshold electron impact doubly differential cross sections for the ionization of neon and xenon

“…For Xe, the most recent measurements have been the (e, 2e) results of Bellm et al [21] who carried out (e, 2e) measurements of Xe with spin-polarized electrons at 112 eV preceding the earlier work of Panajotovic et al [22] at E 0 = 147.8 eV with the aim of investigating the fine-structure effect in the ionization of atoms as compared to their excitation [23] which has been more studied. The latter work of [21] had significantly better precision than the former [22] owing to improved statistics in an effort to provide a more rigorous test of theory. These measurements are made possible by the large fine-structure splitting and the heavy target property of Xe.…”

“…These investigations (which have looked at the valence electron ionization, i.e. with the Xe + core left in the 5 2 P 3/2 or 5 2 P 1/2 state) have shown that including electron exchange terms between the bound and continuum electrons in the scattering, such as the Furness-McCarthy exchange potential [21,22], improved agreement between theory and experiment. Here relativistic effects were included by using a large component of a relativistic wavefunction for the initial distorting potential, so the continuum wave had some bound state relativistic contributions through the Furness-McCarthy exchange potential [24].…”

Electron Scattering by Atoms, Ions, and Molecules

“…Spin-polarized electron beams have also been used in the study of ionization processes, either in ionization asymmetries using a spin-polarized atomic beam as well (see, for example, Baum et al (1993;), or in studies where a p-electron is ejected from a noble gas such as Xe and the fine-structure of the residual ion is resolved (see Bellm et al (2008) and references therein). Finally, relatively few polarized-electron experiments have been performed with molecular targets to date.…”