Electron capture in the 3s level by proton and α-particle from atomic hydrogen

Bates' distortion approximation (see Proc. R. Soc., vol.A247, p.294 (1958)), which takes into account the non-orthogonality of the initial and final wavefunctions, has been applied to investigate the charge-transfer processes involving electron capture into the 3s level from the hydrogen atom by proton and alpha-particle impact. A straightforward method has been developed for evaluating the exchange matrix elements with momentum transfer. The method, which can be extended to higher excited s states without much difficulty, has been verified by applying it to the case of ground-state electron capture by protons from hydrogen atoms. Capture cross sections have been calculated for incident ion energies in the range 25-800 keV. From the same general program the authors have computed the capture cross sections in the other approximations discussed by Bates. The effect of distortion is found to be considerable throughout the energy range considered.