Projectile interactions in theoretical triple differential cross sections for simultaneous excitation–ionization of helium

Abstract

The importance of projectile interactions in triple differential cross sections (TDCS) is explored for the problem of simultaneous excitation–ionization of helium by electron impact using a new approach that we call the four-body distorted wave model (4DW). The 4DW model includes all projectile interactions, namely initial- and final-state projectile–target interactions, and the post-collision interaction between the two continuum electrons. Results are presented for an incident electron energy of 500 eV and are compared to experimental data, as well as a second-order R-matrix theory and the first Born approximation. Results for absolute TDCS ratios of ionization without excitation to excitation–ionization are also presented.

Indistinguishability in electron-impact excitation-ionization of helium

“…[9], and we present only the relevant details here. For an * harrisal@hsu.edu electron incident on a target with two active electrons, there are three indistinguishable electrons involved in the collision.…”

“…In our previously published First Born Approximation (FBA) and 4DWD results [6,9,10], the exchange and capture amplitudes were neglected, and only the direct amplitude was calculated. This effectively labeled the electrons and ignored any indistinguishability.…”

“…During the collision, one of the atomic electrons is ionized and the other atomic electron is left in an excited state of the He + ion. Several years ago, kinematically complete experiments were published for this process [5][6][7], and two basic types of theories were compared with the experimental results [5,6,[8][9][10]. One was a hybrid approach of Bartschat [5] which combined a distorted wave treatment for the fast projectile electron with an R-matrix approach for the bound state and slow electron (DWB2-RMPS).…”

“…One was a hybrid approach of Bartschat [5] which combined a distorted wave treatment for the fast projectile electron with an R-matrix approach for the bound state and slow electron (DWB2-RMPS). The other was a perturbative four-body distorted wave approach (4DW) developed by the authors [9]. Both models were able to partially predict the general features of the experiments, but there were still some discrepancies.…”

The role of projectile interactions in triply differential cross sections for excitation–ionization of helium

“…They have compared their relative experimental data with two different theoretical models, namely, momentum space close-coupling (CCC) and configuration space R-matrix with pseudostates (RMPS) and found the importance of accounting for secondorder effects in the projectile-target interaction. Very recently, Harris et al [4] reported a new model, the four-body distorted wave (4DW) model to study the electron impact excitationionization process of helium. The 4DW model considers all projectile interactions including the initial-and final-state projectile-target interactions and the post-collision interaction between the two continuum electrons.…”