Evidence for a metastable state of the fundamental dianionH2−

A resonance state with three equivalent electrons and one proton has been identified. Large-scale calculations have been performed using the complex-rotation technique, and the results indicate that the investigated ${}_{}{}^4{}_{}{}^{}\mathrm{S}_{}^{\mathrm{o}}{}_{}{}^{}$ state of ${\mathrm{H}}^{2\mathrm{-}}$ is strongly correlated. The findings are rationalized by comparing with bound doubly charged anions, isoelectronic states of the Li atom, and calculations in the infinite-dimension limit. In addition, the emerging picture is sustained by an analysis of the complex-rotated wave function.