Single-centred expansion coupled states calculations are performed with basis sets large enough to achieve convergence. The particular collision system studied is p+H(1s) at energies of 15 keV and above. The results obtained establish the validity of this method for calculating excitation and electron removal cross sections even in situations where charge transfer is large. Cross sections for 1s to 2l', 3l' and 4l' excitation and for electron removal are presented and compared to experiment and to other theoretical calculations.

Single-centred coupled states calculations of cross sections for excitation and ionization of atomic hydrogen by antiprotons are compared to previous calculations and to experiment for projectile energies in the range 1-300 keV. A noticeable disagreement between experiment and theory is found for the antiproton ionization results in the range 30-80 keV.

We present multi-cut forced impulse method cross sections for the single ionization of helium by antiprotons in the energy range 12-200 keV amu −1 . Eight segmented time intervals, bracketed by collapse onto fully correlated states, are needed to establish convergence in the effects of intermediate dynamic correlation. At low energies the theoretical cross sections fail to reproduce experiments. We point out that a similar situation obtains for the antiprotonhydrogen system.We take great pleasure in dedicating this letter to Richard Lemmer on the occasion of his 65th birthday.

Single-centred finite Hilbert basis set calculations, using bases with a substantial number of orbitals, have been shown to accurately reproduce excitation and electron removal cross sections for the p+H(1s) and p+H(n=2) systems. The present paper extends the method to the p+He+(1s) and p+He+(n=2) collision systems at incident projectile energies of 25 keV and above. Cross sections for 1s to 2l', 3l' and 4l', 2s and 2p to 3l' and 4l' excitation and for electron removal from the 1s, 2s and 2p are presented and compared to experiment and to other theoretical calculations.

The independent event model (IEV) is used to calculate single and double electron removal cross sections for p + + He collisions. The single electron removal cross sections are in good agreement with experiment. In contrast to the model of Janev and co-workers, it is found that the single electron removal cross section for p + + He + is much larger than the double electron removal cross section for p + + He, since in small impact parameter collisions of protons with He the probability of removing the first electron is less than unity. Double electron removal cross sections for p + + He calculated in the IEV are found to be in poor agreement with experiment, in contrast to p − + He where good agreement was obtained. For p + + He, the IEV double ionization result is improved somewhat if approximate allowance is made for the screening of the projectile by the electron if it is captured in the first event. The difference in the agreement of the IEV double ionization results with experiment may also indicate a qualitative difference in the role played by electron correlation in these two collision systems.