Selective enhancement of 1s2s2p ⁴P_J metastable states populated by cascades in single-electron transfer collisions of F⁷⁺(1s²∕1s2s ³S) ions with He and H₂ targets

A mechanism for the selective population of 1s2s2p ⁴P_J states by electron capture in energetic collisions of F⁷⁺(1s2s ³S) ions with H₂ and He is elucidated. Capture calculations indicate (1s2s ³S)nl ^2,4L doublet and quartet levels to be approximately evenly populated for n=2–5. Following capture the doublets Auger decay strongly to the 1s² ground state allowing for negligible feeding of other lower-lying doublets by radiative transitions. The quartets, however, find this decay channel blocked by spin conservation and instead radiatively cascade through lower lying quartets, eventually strongly populating the lowest-lying 1s2s2p ⁴P_J levels in agreement with older experimental results for collision energies above 0.7 MeV∕u.