Sequential electron emission and nuclear dissociation after the O 1s→(Σu−4)4pσ excitation in O2 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 Auger electron and ions, we identified the sequences of processes following the spectator Auger decays induced by K-shell excitation in O-2. The first step of the spectator Auger decay can end up to a few metastable O-2(+) states which autoionize into stable O-2(2+). However, the majority of O-2(+) states are dissociative. They evolve into several dissociation limits with complex crossings between potential-energy curves. After the molecular dissociation is finished, the generated fragments can further decay either by fluorescence emission or by autoionization. Interestingly, some electrons are always emitted after molecular dissociation.