Close coupling calculations for massive ion-hydrogen atom collisions in the linear trajectory model

Abstract

The Wilets and Gallaher (1966) formulation for H⁺-H collisions has been generalized to the heavy ion-atomic hydrogen collision. The resulting coupled differential equations have been solved and a corresponding computer program has been constructed to extract numerical results. Four-state calculations have been carried out for the specific example of He²⁺-H collisions using both eigenfunction and pseudo-state expansion bases. Charge transfer, excitation and ionization cross sections as well as 2p polarization fractions are presented and compared with other theoretical calculations and experimental measurements where these are available. The computations encompass the range of He²⁺ energies from 6.3 keV-4 MeV. It has been found that: the neglect of rotational coupling effects underestimate charge transfer cross sections at impact energies of the He²⁺ ion less than about 15 keV; at high velocities of encounter the charge transfer cross section to the He⁺(1s) state predominates over that to the He⁺(2s) or He⁺(2p) state and is confined to a small range of impact parameters; excitation cross sections are sensitive to the choice of pseudostates. It is further shown that an eigenfunction expansion basis is unlikely to reproduce the 1.2 degrees total charge transfer probability experiment of Keever and Everhart (1966) in a calculation employing a four-state approximation.