Continuum-distorted-wave calculations for rearrangement cross sections and their sensitivity to improvements in the target wave function: Proton-helium collisions

The continuum-distorted-wave (CDW) approximation has been used to calculate the electron-capture cross sections $Q\left(\mathrm{nl}\right)\mathrm{}$ when a fast proton collides with a helium target atom. The range of the projectile energy is from 25 keV to 3 MeV and the electron-capture states considered are $nl=1s, 2s, \mathrm{and} 2p$. Of specific interest here is the sensitivity of these cross sections with respect to a systematic improvement in the description of the target ground-state wave function, both up to and beyond the Hartree-Fock level. Large changes were found to occur in the magnitude of each $Q\left(\mathrm{nl}\right)\mathrm{}$ as we progress from a simple one-parameter wave function for He up to a configuration-interaction description: The latter wave function accounted for about 99% of the electron correlation energy. Values of the total capture cross section were determined and compared with experiment over the available energy range of 100-2990 keV. The correlated results were, overall, in good agreement with experiment—especially in the high-energy region.