Channel-coupling, target-structure, and second-order effects in electron-impact ionization of Ar ( 3 p ) and Ar ( 3 s )

The importance of second-order effects in the projectile-target interaction, channel coupling in the ejected-electron-residual-ion interaction, and multiconfiguration effects in the target description is investigated for electron-impact ionization of argon. For incident projectile energies of 200 and 113.5 eV, a scattering angle of 15 deg., and ejected-electron energies between 2 and 20 eV, we find a strong sensitivity of the theoretical predictions to the target structure, channel coupling, and the proper treatment of nonlocal exchange. In some cases, accounting for these effects seems more important than extending a local-exchange, single-configuration distorted-wave theory by including the accurate three-body Coulomb asymptotic boundary condition. Despite encouraging improvement in agreement between our predictions and recent experimental results in some cases, severe discrepancies remain in others. More experimental data, preferably absolute but at least cross-normalized to each other for a variety of kinematic conditions, seem necessary to further guide ongoing theoretical efforts.