Many-body theory of electron scattering by excited atomic targets: Electron-impact-induced transitions 21,3S→n1,3L(L=0,1,2;n=2,3,4) in helium

A many-body-theory (MBT) formulation for electron scattering by excited electronic states is applied to excitation from the 2 ${}_{}{}^{1,3}{}_{}{}^{}$S metastable states of helium. The lowest-order MBT for these transitions involves a ‘‘chanel coupling’’ to the ground state of helium as well as a distortion of the free-electron wave function by the ground state of the target, while the distorted-wave approximation (DWA) involves a distortion of the incident and scattered electron wave functions by the initial and final target states, respectively. Results using the first-order many-body theory and DWA are reported here for integral and differential cross sections for excitation from the 2 ${}_{}{}^{1,3}{}_{}{}^{}$S states to (2,3) ${}_{}{}^{1,3}{}_{}{}^{}$P, 3 ${}_{}{}^{1,3}{}_{}{}^{}$S, and 3 ${}_{}{}^{1,3}{}_{}{}^{}$D states, and are compared with published experimental and theoretical data.