A 29-state R-matrix investigation of resonances in e--He scattering at low energies. I. On the convergence of the calculations of 11S-23,1S excitation cross sections

Fon and Lim (1990) have reported the 11-state and the 19-state R-matrix calculations of 1 1 S-2 3 S differential cross sections at low energies. The discrepancy between the R-matrix calculations at scattering angle 90º and the experiments remains at 20%. Another attempt has been made here to reduce the discrepancy. Sawey et al. (1990) reported a 29-state R-matrix calculation on the collision strengths for the 1 1 S-2 3,1 S excitations and an error in their representation of the 19-state collision strengths, which were wrongly shown to be significantly higher than the 29-state results, is corrected. In this paper, the same 29-state R-matrix calculation of Sawey et al. is extended to obtain 1 1 S-2 3,1 S excitation cross sections at 500 energies ranging from the 2 3 S threshold to 24.2 eV for scattering angles 30, 55, 60, 90, 120, 125 and 140 degrees. The convergence of the R-matrix calculations in shape and magnitude of the cross sections is re-examined.