COULOMB 3-BODY EFFECTS IN ELECTRON-IMPACT IONIZATION OF ARGON

Triple differential cross sections have been measured for the electron impact ionization of a 3p shell of argon in coplanar geometries. Resu lts are presented for 40, 20, 8, and 2 eV excess energy with respect t o ionization threshold, this energy being equally shared between both outgoing electrons in the final state. Comparison is made with distort ed wave Born approximation calculations that include initial channel p olarization and final channel post-collisional interaction. Results ar e shown to be very sensitive to few-body effects in both incident and final channels; however, agreement remains poor and the experimental r esults present a substantial challenge to theory.