Electron capture from hydrogen negative ions and a study of electron correlation in momentum space.

In Part 1 the effect of electron correlation on the one- and two-particle momentum distributions for the iso-electronic systems H-, He and Li+ is analysed by using the natural expansion representation of a configuration-interaction space wavefunction. The Compton profiles are examined and, in addition, several expectation values are reported with emphasis being given to two-electron properties. In particular, the angular and radial components of correlation are assessed by the determination of various correlation coefficients. The introduction of total angular correlation is found to increase the probability of the two momentum vectors being aligned - as is indicated by the positive values obtained for the angular correlation coefficients. By contrast, the radial coefficients revealed negative correlation effects. Where possible we compare our results with those of other authors. In Part 2, the H- ion is considered as a target from which high energy electron capture can occur. Using the continuum distorted wave approximation, cross sections o(ne, n' e') are determined for the reaction H+A + H-B(1s2) → HA (ne) + HB (n'e') where the range of projectile energy extends up to 10 MeV and ne = 1s, 2s, 2p and n'e' = 1s, 2s. Cross sections were also calculated for electron capture from H- by fast alpha-particles and micro+-mesons. 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 wavefunction. Very large changes were found to occur in the magnitudes of each o(ne, n'e') as we progress from a simple one-parameter wavefunction for H- up to a configuration interaction wavefunction; the latter wavefunction accounted for over 99% of the correlation energy. The sensitivity of the cross sections to the description of the target wavefunction in the limit of high impact velocity is discussed in some detail.