Sequential electron emission and nuclear dissociation after the O 1s -> ((4)Sigma(-)(u))4p sigma excitation in O-2 molecules

When an electron is resonantly excited from a core orbital to a Rydberg one in a molecule, complex multi-time-scale multi-step processes are triggered. By using a high-resolution energy-resolved coincidence between Augerelectron and ions, we identified the sequences of processes following the spectator Augerdecays induced by K-shell excitation in O-2. The first step of the spectator Augerdecay can end up to a few metastable O-2(+) states which autoionizeinto stable O-2(2+). However, the majority of O-2(+) states are dissociative. They evolve into several dissociationlimits with complex crossings between potential-energy curves. After the molecular dissociationis finished, the generated fragments can further decay either by fluorescence emission or by autoionization. Interestingly, some electrons are always emitted after molecular dissociation.