Triple-center treatment of electron transfer and ionization inHe2+-H andp-He+collisions

Cross sections have been calculated for electron transfer into the 2s, 2$p_0$, 2$p_1$, and all states of ${\mathrm{He}}^{+}$, and for ionization, in collisions between ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{2+}{}_{}{}^{}$ ions and H(1s) atoms. Cross sections have also been calculated for electron transfer into the ground state and all states of H, and for ionization, in collisions between protons and ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$(1s) ions. The center-of-mass collision energies range from 1.6 to 40 keV. A coupled-state approach is taken using large triple-center bases of up to 34 states centered on the two nuclei and a third center chosen to be the equiforce point (saddle point of the potential) between the nuclei. The sensitivity of the cross sections to the size of basis is studied, and the ionization cross sections are found to be the more sensitive, particularly at lower energies. The electron-transfer cross sections in most cases are found to agree extremely well with larger-basis molecular-state results at generally lower energies and with double-center pseudostate results at higher energies, as well as with experimental results. The more sensitive ionization cross sections follow the trend of the experimental data, suggesting the considerable importance of saddle-point electrons as previously observed for p-H collisions.