Electron-impact ionization of the helium metastable 23S state

By performing multi-core electron–helium Born calculations we present a systematic study of the high-energy behaviour of the 2 3 S total single ionization cross section which takes into account autoionization and ionization with excitation processes. We found that our results are in substantial disagreement with the previously reported Bethe–Born results of Briggs and Kim (1971 Phys. Rev. A 3 1342–9). We have also performed new close-coupling calculations within the frozen-core model and used them together with the multi-core Born calculations to establish theoretical estimates over the entire energy range of interest. At low energies the cross sections are only marginally higher than the other recently reported theoretical results, and therefore still substantially below the experimental data of Dixon et al ( 1976 J. Phys. B: At. Mol. Phys. 9 2617–31 ). At high energies we find that the multi-core calculations lead to significantly higher cross sections than the corresponding frozen-core calculations. However, as at the lower energies, experiment still remains substantially above the latest theory.