The ionization and excitation cross sections of atomic hydrogen with antiprotons are calculated using the close-coupling method, where the wave function is expanded by atomic states only on protons. The resulting total cross sections are in good convergence and in agreement with other calculations based on the closecoupling method with considerably large basis set. The angular distribution of ionized electrons is calculated by substituting the obtained wave function in the close-coupling method into the integral form of the transition amplitude. Above 100 keV, the angular distributions of ionized electrons are compared for proton-and antiproton impacts.

Using a unified theoretical treatment of different ionization processes occurring in photon and electron impact on atoms and ions, we examine lithium near its 'hollow-atom' threshold. By introducing a set of 'core base states' for the Li + target, and optimizing the collisional representation within an R-matrix model, we combine ab initio, outer-and innershell effects, excitation and ionization channels, direct and indirect ionization processes, resonant and non-resonant behaviour, for photon and electron impact processes. We use the method to interpret experimental data on electron impact ionization of ground state Li + and photoionization of Li, and look at double photoionization of Li and electron impact ionization out of metastable Li + . We examine and quantify hollow-atom interference effects and resonances, tabulating all 480 2l2l nl states for n 9, l 3, and show the chaotic behaviour of overlapping series.

We have applied close-coupling calculations to calculate the single-ionization cross section of helium by antiproton impact at collision energies above 10 keV. The atomic states of helium are expanded by three sets of eigenstate͑s͒ of He ϩ : ͕1s͖, ͕1s,2s,2p͖, and ͕1s,2s,2p,3s,3p,3d͖. The calculations are in good convergence within these models. The present cross sections are in good agreement with the experimental data of Andersen et al. ͓Phys. Rev. A 40, 7366 ͑1989͒; 41, 6359 ͑1990͔͒ and Hvelplund et al. ͓J. Phys. B 27, 925 ͑1994͔͒ at energies above 40 keV. However, our treatment gives larger cross sections than the data of Hvelplund et al. for lower energies and the disagreement is no less than a factor of 2 near 10 keV.

The Dirac R-matrix theory is used to calculate the collision strengths for electron impact excitation of He-like ions (S 14+ , Ca 18+ and Fe 24+ ) using the Dirac atomic R-matrix code, which has been developed mainly by Norrington and Grant (Norrington P H and Grant I P 1987 J. Phys. B: At. Mol. Phys. 20 4869). The lowest 31 target levels are included in the calculation. Rate coefficients are obtained for transitions from the ground 1s 2 1 S 0 state to the fine-structure levels of all excited states of 1s2 ( = 0, 1) and 1s3 ( = 0, 1, 2) configurations. We compare our results for rate coefficients with the results of previous calculations, and indicate where significant differences arise because of our more accurate representation of resonance and relativistic effects.

Abstract. Electron excitation collision strengths of 3d2 fine-structure transitions in Ca-like Fe vii are calculated using an R-matrix method, which included the 80 terms arising from the 3d 2 , 3d4s, 3d4p, 3d4d, 3d4f and 3p 5 3d 3 configurations. Extensive autoionizing resonance structures together with channel coupling is therefore explicitly included; relativistic effects are accounted for by a term-coupling transformation. A thermal average is taken to obtain the effective fine-structure collision strength as a function of electron temperature T , for log T (K) = 4.3−6. Open 3p-shell resonances are seen to considerably enhance the background collision strength, by several factors for some of the 3d 2 j→j transitions.