Amplified Collective Auger Decay of Double Inner-Shell Vacancy in Xe

The collective Auger decay (CAD) of Xe2+ 4d-2 double core-hole states in which two outer-shell electrons fill the double inner-shell vacancies while releasing a third energetic Auger electron is explored using multi-electron-ion coincidence spectroscopy. The CAD branching ratio relative to the total Auger emission of Xe2+ 4d-2 states is estimated to be 2×10-2±1×10-2, surpassing the branching ratios of previously reported CAD paths by a factor of 10 or more. This amplified CAD in Xe2+ 4d-2 states is primarily attributable to their near-degeneracy with intermediate configurations required to promote CAD in second-order perturbation theory. Such near degeneracy is characteristic of all double inner-shell vacancy states in medium and heavy elements, suggesting that CAD paths play a more pivotal role in the relaxation of core-excited matter than is currently understood.