Electron capture by multiply charged ions on helium target a population mechanism for minor channels

The paper reports on differential cross sections at keV energies for electron capture by various ions of charge q<9 colliding with helium atoms. Whereas the cross section for single capture into the principle quantum number n, the dominant process, is peaked near zero degrees, the cross section for capture into n+1, a less exothermic process, is peaked at large scattering angle. The process involves a population scheme taking place at small internuclear distance. This mechanism was predicted by the 'electron promotion model'.