Electron excitation from the 11S, 23S and 21S states of helium. An eleven-state R-matrix calculation

Abstract

An R-matrix calculation for electron-helium scattering is described in which the eleven lowest target states of helium are included, using configuration interaction wavefunctions. Excitation cross sections are calculated up to 30 eV from the 11S ground state and the metastable 23S and 21S states of helium to the higher n=2 states, and, for the first time in an ab initio calculation, to the n=3 states. The authors confirm their preliminary finding that the explicit coupling of the n=3 channels significantly reduces the cross sections calculated in an earlier five-state approximation, by up to 50% for n=1 to n=2 transitions at energies above the n=3 thresholds. Using the new cross section data, rate coefficients are calculated for temperatures up to 50000K for the transitions considered.