Electron capture and excitation in H⁺-He (1s2s; ¹,³S) collisions.

The electron capture and excitation processes in collisions of H⁺ with excited He.(1s2s; ¹,³S) atoms are investigated theoretically by using the two-centre atomic orbital close-coupling method in the energy range 2.200 keV u^-1. The interaction of active electrons with the target ion is represented by a model potential different for the singlet and triplet systems of He states. In the electron capture studies, the basis included all the He (1s, n ≤ 6) discrete states and all the H (n ≤ 7) states plus 202 pseudostates, while for the excitation studies all the He (1s, n ≤ 8) states plus 244 pseudostates and all the H (n ≤ 5) discrete states were included in the basis. The excitation cross section results of the present calculations are compared with other theoretical results and good agreement is obtained at high collision energies. For energies below 6 keV u^-1, the present excitation and electron capture results are compared with those from the recent quantal molecular orbital close-coupling calculations showing good agreement for the dominant channels. It is found that the cross sections for excitation and state-selective electron capture are significantly different for the singlet and triplet states, particularly in the low-energy region. [ABSTRACT FROM AUTHOR]