The calculation of high energy electron-capture cross-sections using the continuum distorted wave (CDW) and continuum intermediate states (CIS) methods

The CDW transition amplitude is derived for electron-capture from a two-electron target by a bare nucleus. Total capture cross-sections are evaluated for H+ and He2+ incident on Li+ over an impact energy range of 100 keV <= E <= 3000 keV and 100 keV <= E <= 10 MeV, respectively. The effect on the cross-sections of introducing electron-correlation into the Li+ wavefunction is examined, and the total cross-sections are compared with experimental data. The CDW method is then generalised to the case of a many-electron target atom, and cross-sections for electron-capture by fast protons from the Li atom, and its related ions, are calculated. A procedure for determining the effective screening of the target nucleus is presented and applied to the Li and Li+ systems. The CIS method is presented, and its merits for application to the more general cases of ion-atom collisions is discussed. (author)