MANY-BODY THEORY OF ELECTRON-SCATTERING BY EXCITED ATOMIC TARGETS - ELECTRON-IMPACT INDUCED TRANSITIONS 2(1,3)S-]N(1,3)L (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 1,3S 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 1,3S states to (2,3) 1,3P, 3 1,3S, and 3 1,3D states, and are compared with published experimental and theoretical data. © 1995 The American Physical Society.