Electron spectroscopy of multiple ionization of argon by electron impact

Doubly differential cross sections (DDCS) for electron ejection in electron-argon collisions have been studied for ejected electron energies 25 to 300 eV, ejection angle ${\theta }_{\delta }=90\mathrm{}°$, and incident electron energies of 300 eV to 8 keV. Performing a charge-state analysis of the recoil ion in coincidence with the ejected electron, we were able to distinguish between singly and multiply ionizing collisions. It was observed that the relative importance of multiple ionization events increases with increasing energy of the ejected electron. At an ejected electron energy corresponding to $\mathrm{LMM}$ Auger transitions, ${\mathrm{Ar}}^{2+}$ and ${\mathrm{Ar}}^{3+}$ are predominantly produced by $L$-shell ionization. From an analysis of the corresponding DDCS, information about simultaneous $L$- and $M$-shell ionization is obtained.