Probing the mechanism of simultaneous two-electron emission on core-hole decay

Simultaneous two-electron emission upon 2p core-electron excitation in Ar has been studied using a state-of-the-art multielectron coincidence method. Simultaneous two-electron emission effectively populates Rydberg-excited Ar2+ states, in which the excited electron behaves as a spectator of the direct double Auger decay of the core hole. This observation constitutes experimental evidence that the shake-off mechanism is not sufficient to model direct double Auger decay of a 2p hole in Ar and suggests an important contribution from the knock-out mechanism.