Ordering of cross sections for electron capture from He-like targets by fast projectiles

The continuum-distorted-wave (CDW) method is used to determine total electron-capture cross sections Q=Σnl^σ[nl] for proton and α-particle projectiles incident on Li⁺ in energy ranges of 100≤E≤3000 keV and 100≤E≤10000 keV, respectively. A configuration-interaction (CI) wave function is used to describe the Li⁺ electrons; for comparison, capture cross sections for H^- and He are examined. For each system the percentage change in Q, Δ(HF→CI), is given for progression from a Hartree-Fock (HF) to a CI description of the target electrons. The main emphasis in this work is devoted to a rationalization of the trends observed in the ordering of Q for these three targets. This was achieved by an analysis of the CDW expression for an individual capture cross section σ[nl, n^'l^'], where nl and n^'l^' are the states of the "active" (captured) and "passive" electrons, respectively.