Electron transfer in collisions of He++ ions with H atoms at 4He++ impact energies of 0.1-20.0 keV

Total cross sections have been calculated for electron transfer into all states of He+ during collisions of He++ ions with H atoms at 4He++ energies from 0.1 to 20.0 keV. The coupled molecular-state approximation that is used incorporates in the basis up to 20 states 1ssigma, 2ssigma,...,4fphi of the frozen HeH++ molecule. Convergence of cross sections with respect to the size of the bound-state basis is studied; at 8 keV, the eight states 1ssigma, 2psigma, 3dsigma, 4fsigma, 2pπ, 3dπ, 4fπ, and 3psigma of the 20 states considered have been found sufficient to determine the 20-state cross section to within a few percent. The nuclei are assumed to follow classical paths, some estimate being made of the effect of nonrectilinear motion at the lower energies. A comparison is made with experimental results, and agreement with most of the recent experimental results is found to be excellent down to about 8 keV; at lower energies, the theoretical cross section falls off rapidly with decreasing energy, in contrast to the single early low-energy measurement