Topology of the adiabatic potential energy surfaces for the resonance states of the water anion

The potential energy surfaces corresponding to the long-lived fixed-nuclei electron scattering resonances of H₂O relevant to the dissociative electron attachment process are examined using a combination of ab initio scattering and bound-state calculations. These surfaces have a rich topology, characterized by three main features: a conical intersection between the ²A₁ and ²B₂ Feshbach resonance states; charge-transfer behavior in the OH0.2em0ex(²Π)+H^- asymptote of the ²B₁ and ²A₁ resonances; and an inherent double-valuedness of the surface for the ²B₂ state the C₂ᵥ geometry, arising from a branch-point degeneracy with a ²B₂ shape resonance. In total, eight individual seams of degeneracy among these resonances are identified.