Double Ionization of Helium by Fast Electron Impact

Abstract

Double ionization of He by 3-keV electron impact is explored in a kinematically complete experiment. The 12-dimensional, 4-particle final-state momentum space is mapped for two slowly ejected electrons $({\mathbf{k}}_{b,c}<1.2\mathrm{a}.\mathrm{u}.)$, the ${\mathrm{He}}^{2+}$ ion $({\mathbf{k}}_{\mathrm{He}}<5\mathrm{a}.\mathrm{u}.)$ and the fast electron for all relative emission angles and energy partitions. Different reaction mechanisms are identified by examining the angular correlation between the slow electrons as a function of the momentum transfer. A fivefold differential cross section is presented for asymmetric energy sharing in coplanar geometry.