Sequential electron emission and nuclear dissociation after the O \(1s→({}^4\Sigma^{−}_{u})4pσ\) excitation in O₂ molecules

Abstract When an electron is resonantly excited from a core orbital to a Rydberg one in a molecule, complex multi-time-scale multistep 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 O₂. The first step of the spectator Auger decay can end up to a few metastable O₂⁺ states which autoionize into stable O₂²⁺. However, the majority of O₂⁺ 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