Differential ionization cross-section calculations for hydrogenic targets with Z⩽4 using a propagating exterior complex scaling method

A propagating exterior complex scaling method, with iterative coupling, has been adapted for the electron impact of charged hydrogenic targets. Using this fully ab initio method for solving the Schrödinger equation, which has no uncontrolled approximations, we present highly accurate total, single-differential, double-differential, and triple-differential cross-section calculations for the electron-impact ionization of hydrogenic targets with nuclear charge Z⩽4 (H, He⁺, Li²⁺, Be³⁺). For a fixed scaled energy, the total and differential cross sections begin to converge with respect to increasing Z when scaled by Z⁴ and Z⁶, respectively, and converge more rapidly with increasing incident-electron energy. The angular distributions of the differential cross sections change systematically with increasing nuclear charge for energies above the peak total ionization cross section, but for some lower-energy kinematics the triple-differential cross section for charged targets is significantly different from that of atomic hydrogen.