Formation of lithium-like boron and nitrogen ions in the 4 P 5/2 state in gaseous media

We experimentally determined the fraction of αv of lithium-like boron B2+ and nitrogen N4+ ions in the 4 P 5/2 state having a velocity of 3.6 au that are formed upon capture of two (α2) electrons by hydrogen-like B4+ and N6+ ions and upon capture of one (α1) electron by helium-like (1s2s)1,3 S metastable B3+ and N5+ ions in gaseous media (H2, He, N2, Ar), as well as upon passage through a celluloid film. In light-element media (H2, He), α2 increases proportional to the target thickness T g and reaches a maximum at T g ≈ 1016 atom/cm2 (for B ions, α2 ≈ 0.2 in H2 and α2 ≈ 0.4 in He). For boron and nitrogen ions passing through thin layers of heavier gases (N2, Ne), α2 depends considerably more weakly on T g , and, in Ar, becomes practically constant. It is assumed that, since hydrogen and helium do not contain electrons with parallel spins, autoionizing lithium-like ions are formed as a result of successive (one by one) capture of electrons, whereas, in the heavier gases, simultaneous capture of two electrons predominates. At T g ∼ 1015 atom/cm2, the fraction α1 of boron ions is the highest in He, ∼0.15, and the lowest in Ar, ∼0.07, being in qualitative agreement with calculations.