Excitation of the 3D states of helium by electrons and positrons

Abstract

Distorted-wave approximation calculations were carried out for the electron-impact excitation of 31,3D states from the 11S ground state of helium. Results are presented at an electron energy of 40 eV for the Stokes parameters P1-P4; coherence parameters Pl, γ, [Formula: see text], ρ00; and differential cross sections where most other theoretical and experimental data are available for comparison. The calculation is further extended to the positron-impact 11S–31D excitation in helium and comparison with the corresponding electron-impact results is discussed.