Electron impact cross sections for multiple ionization of Ar: detector gain effects revealed

Partial cross sections were measured for the ionization Ar + e → Arn+ + (n + 1) e for n = 2-5 as a function of electron energy (0-660 eV). Although recent investigations are in agreement with regard to the absolute cross sections for single ionization, large discrepancies still exist for multiple ionization. Our results support the measurements of some authors but disagree with other recent studies which invariably obtain larger cross sections. These discrepancies are attributable to the dependence of electron multiplier gain on ion impact energy and, therefore, ion charge. The cross sections presented here for Ar4+ and Ar5+ have not been previously measured. (author)