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.