Dark-State-Mediated Low-Energy Electron Attachment to Molecular Oxygen: Symmetry Adapted Decomposition of the DEA Resonance through Dyson-Orbitals’ Incoherent Mixing

Dissociative electron attachment (DEA) to O2 exhibits a prominent resonance peak at ∼6.5 eV, producing O– with a single kinetic energy band (∼1.5 eV) and a distinct four-lobed angular distribution. Using velocity-map imaging and complex absorbing potential equation-of-motion electron-attachment coupled-cluster singles and doubles (CAP-EOM-EA-CCSD) calculations, we notice that this resonance is mediated by electron-impact excitation to the optically dark a1Δg and b1Σg+ states, which suggests electron impact excitation to these optically dark excited states provides an appropriate electronic structure for electron attachment forming 2Πu, 2Πg and 2,4Σu Feshbach resonances. The measured angular distribution is reproduced by an incoherent superposition of three symmetry channels: 2Πu (66.5%); 2Πg (25.1%); and 2,4Σu (8.5%). The Dyson orbitals computed from the CAP-EOM-EA-CCSD calculations quantitatively reproduce the channel weights and their energy dependencies. This dark-state-mediated mechanism pinpointedly resolves the experimental observations and provides a general symmetry-adapted framework for decomposing DEA resonances from the fragmented anions angular distributions.