Role of the postcollision interaction in electron-impact ionization of argon and krypton

There has been impressive progress in the theoretical treatment of electron collisions with atoms in the last decade. As a result, the fundamental collision problems of electron-hydrogen or electron-helium scattering are now understood fairly well. For heavier atoms, an accurate treatment of atomic ionization remains more elusive than atomic excitation due to the final-state three-body Coulomb problem. For higher impact energies, the first-order distorted-wave Born approximation is typically in reasonable agreement with fully differential cross sections (FDCS) for ionization. However, FDCS measurements are starting to be reported for lower incident electron energies and here agreement between experiment and theory is not good. In this paper we examine the importance of exchange distortion and the final-state electron-electron interaction on these collision processes.