Exchange effects in low energy electron impact ionization of the inner and outer shells of argon

Abstract

First order distorted wave Born approximation (DWBA) triple differential cross sections are reported for low-energy electron-impact ionization of the inner 3s and outer 3p shells of argon. Previous DWBA works have demonstrated that experiment and theory are not in accord for low energy ionization of inert gases and here we investigate the importance of exchange scattering. Different approximations for treating exchange scattering are investigated. It is shown that exchange scattering is particularly important for 3s ionization. Even with a proper treatment of exchange, the first order calculations are still not in satisfactory agreement with experiment. Consequently higher order effects will have to be included to achieve a satisfactory description of the low-energy ionization process. We also investigated both the Hartree-Fock and optimized potential methods for calculating atomic wavefunctions and static potentials and found that both methods produced almost the same cross sections.

Triple differential cross section in (e, 2e) collisions for sodium in a coplanar symmetric geometry

“…The DWBA and DWBAP calculations of Hitawala et al clearly overestimate the experiment in the backward scattering region, and their TDCS in the range θ < 25 • increase monotonically as the scattering angle decreases. In fact, in such coplanar symmetric geometry, the repulsion between two outgoing electrons is strong when the scattering angle becomes very small, so the TDCS should go to zero at θ ∼ 0 • [34]. The present two DWBAPCI calculations with MSCEP and SASEP both reproduce the correct shape to the experiment but give slight shift by about 5 • to the forward peak towards higher scattering angle and to the backward one towards lower scattering angle, respectively.…”

Comparison of theoretical and absolute experimental fully differential cross sections for ion-atom impact ionization

“…The important remaining questions are mainly concerned with nearthreshold ionization of hydrogen and this problem has recently attracted intense interest and controversy (Bencze and Chandler 1999, Bray 1999, Stelbovics 1999, Rescigno et al 1999, Bray 2000, Bray et al 2001, Baertschy 2002). The situation is much different for electron-impact ionization of the heavier inert gases where experiment and theory are not in good accord for incident electron energies below about 100 eV (Haynes and Lohmann 2001aand 2001b, Biava et al 2002. It should be noted that the different theoretical methods discussed in the above cited papers all give essentially identical total ionization cross sections.…”

An energetic (e, 2e) reaction away from the Bethe ridge: recoil versus binary

“…The noble gas atoms are attractive candidates for this research because of a relatively simple closed-shell electronic structure. In the past decade, the (e,2e) reaction, in both the symmetric and the non-symmetric kinematics, was measured extensively on Ne, Ar and Xe valence shells at an incident energy typically 10 times larger than the corresponding ionization potential (Haynes and Lohmann 2000, 2001a,b, Biava et al 2002, Haynes et al 2003, Stevenson et al 2005, 2009, Stevenson and Lohmann 2006. Various theoretical models were applied to describe these experimental data: the distorted wave Born approximation 4 Author to whom any correspondence should be addressed.…”