Observation of strong two-electron-one-photon transitions in few-electron ions

Abstract

We resonantly excite the K series of O5+ and O6+ up to principal quantum number n = 11 with monochromatic x rays, producing K-shell holes, and observe their relaxation by soft-x-ray emission. Some photoabsorption resonances of O5+ reveal strong two-electron-one-photon (TEOP) transitions. We find that for the [(1s2s)(1)5p(3)(/2)](3/2;1/2) states, TEOP relaxation is by far stronger than the radiative decay and competes with the usually much faster Auger decay path. This enhanced TEOP decay arises from a strong correlation with the near-degenerate upper states [(1s2p(3)(/2))(1)4s](3/2;1/2) of a Li-like satellite blend of the He-like K alpha transition. Even in three-electron systems, TEOP transitions can play a dominant role, and the present results should guide further research on the ubiquitous and abundant many-electron ions where electronic energy degeneracies are far more common and configuration mixing is stronger.