Excitation of1S(1s,3s) state of helium by electron impact in the Glauber approximation

Abstract

The authors report Glauber cross sections for the electron-impact optically-forbidden transition 1S(1s,3s) from 1S(1s)2 in helium in the incident energy range 29.2 to 500 eV. The Glauber amplitude is calculated using an alternative procedure for the evaluation of the modified Lommel function instead of the usual series presentation which requires very high precision arithmetic for the intermediate values of the argument. The present results for both the differential and integral cross sections in the single-particle Glauber approximation (SPGA) and the full Glauber approximation (GA) are compared with experimental findings and with the predictions of recent theoretical calculations. They find that the GA predicts the shape of differential cross sections even at a few electron volts beyond threshold. At higher incident energies the GA yields cross sections in good agreement with experiment. At low energies the SPGA deviates strongly from the GA and fails to predict the angular distributions of scattered electrons.