INITIAL-STATE, FINAL-STATE AND HIGHER-ORDER EFFECTS IN ELECTRON-IMPACT IONIZATION OF HELIUM-ATOMS

An approximate method to include second-order effects in the treatment of electron impact ionization processes within a combined distorted w ave Born approximation (DWBA)+R-matrix approach is presented. The sens itivity of the results for tri?le differential cross sections for elec tron impact ionization of helium to the description of the initial and final states, and to the inclusion of second-order effects within the R-matrix box, is analysed. It is found that changes in the representa tion of the initial bound state have the strongest effect on the theor etical predictions.