Sturmian treatment of excitation and ionization in high-energy proton-helium collisions

Cross sections have been calculated for excitation of the (2${\mathit{s}}^2$) ${}_{}{}^1{}_{}{}^{}$S, 2 ${}_{}{}^1{}_{}{}^{}$S, and 2 ${}_{}{}^1{}_{}{}^{}$P states and ionization of helium by MeV-energy protons. The sensitivity to couplings among these excitation and ionization channels is studied using the Sturmian-pseudostate approach applied previously by Winter [Phys. Rev. A 35, 3799 (1987)] to one-electron systems. The inclusion of many states greatly lowers the 2${\mathit{s}}^2$ cross section and brings it closer to the recent experimental result of Giese et al. [Phys. Rev. A 42, 1231 (1990)].