We have performed extensive close-coupling calculations to obtain total impact ionization cross sections of He atoms by antiprotons at energies from 1 keV to 300 keV by expanding the time-dependent two-electron wave functions in terms of helium eigenstates. The stability of the calculated ionization probabilities and total ionization cross sections with respect to the choice of basis functions has been examined. Our total ionization cross sections are only slightly higher than the results from the forced-impulse approximation of Reading et al. ͓J. Phys. B 30, L189 ͑1997͔͒ but they disagree with the existing experimental data below 40 keV ͓Hvelplund et al., J. Phys. B 27, 925 ͑1994͔͒. We conclude that new measurements for the ionization of He by antiprotons are needed in the low-energy region.

Abstract. Electron capture cross sections in collisions of C 3+ ions with atomic hydrogen have been studied using the close-coupling two-centre atomic orbital (AO) expansion method by treating the collision system in a quasi-two-electron model. Total electron capture cross sections to the dominant individual singlet and triplet excited states are calculated over the energy range 0.1-50 keV amu −1 . The results are compared with existing experimental data and with theoretical calculations based on the molecular orbital (MO) expansion method. It is found that our AO results are in general agreement with the MO results of Errea et al (1991 J. Phys. B: At. Mol. Opt. Phys. 24 4061) and with experiments but that discrepancies still exist in the details.

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We calculated the total electron-capture cross section for collisions of C 4ϩ ions with atomic hydrogen in the energy range of 10-2000 eV/nucleon using the close-coupling two-center atomic orbital expansion method. Various basis sets have been used to check the convergence of the calculation and the results are shown to be in general agreement with existing experimental data. However, we found no evidence of a dip in the total electron-capture cross sections near 500 eV/nucleon as reported by Bliek et al. ͓Phys. Rev. A 56, 526 ͑1997͔͒.

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