Excitation and ionization of Li+ by electron impact: an R-matrix with pseudo-states calculation

The intermediate-energy electron impact excitation and ionization of helium-like Li+ is investigated using the R-matrix with pseudo-states (RMPS) method. The eleven states with a principal quantum number n≤3 are explicitly included in the calculation. These real states are augmented by 34 pseudo-states with angular momenta in the range zero to three, in order to span the intermediate-energy region in the neighbourhood of the ionization threshold. The RMPS excitation results are compared with a previous 19-state R-matrix (RM19) calculation. The two theoretical calculations are in very good agreement up to the n=3 thresholds. This is not the case in the intermediate region where, in particular, the RMPS results are shown to avoid the large pseudo-resonances of the RM19 calculation. The RMPS results are also found to be in good agreement with the experimental results of Rogers et al for excitation to the 23P state, when corrections due to cascading from higher states and the finite width of the electron beam are taken into account. An estimation of the cross section for single ionization is also made and found to be in good relative agreement with the experimental results of Muller et al. (author)