Excitation from metastable 23S states of helium by electrons and positrons

Abstract

Our recent distorted-wave approximation calculation for the electron-impact excitation cross sections of the helium atom from its 23S state to upper states was extended to obtain alignment and orientation parameters for n3P (n = 2, 3, 4) excitations. Further, similar results are obtained by considering the excitation by impact of positrons. The calculated alignment and orientation results are compared with the only available theoretical electron-impact results obtained using first-order many-body theory.