Model sensitivity of theoretical results for ionization-excitation of helium

The total cross section for ionization and simultaneous ionization-excitation of helium by electron impact has been revisited within the framework of first-order approximations for the projectile-target interaction. A systematic study of the sensitivity of theoretical results on the details of the computational model, specifically the treatments of the projectile-target interaction, the initial bound state and the ejected-electron-residual-ion interaction reveals the difficulties of making highly reliable predictions