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 ${\mathrm{O}}_2$. The first step of the spectator Auger decay can end up to a few metastable ${\mathrm{O}}_2{}^{+}$ states which autoionize into stable ${\mathrm{O}}_2{}^{2+}$. However, the majority of ${\mathrm{O}}_2{}^{+}$ 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.

• Received 18 October 2018

DOI:https://doi.org/10.1103/PhysRevA.99.022511