Strongly bound metastable states of B2+2

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Abstract
The stabilities of about 25 electronic states of B2+2 have been investigated using a multireference CI (MRD‐CI) method and an AO basis set composed of 6s4p2d contracted Gaussian species per atom, including semidiffuse functions relevant for an adequate description of charge transfer interactions. The ground state X1∑+g (σ2gσ2u) is repulsive, as expected by its electronic configuration with a zero bond order. In spite of this and the doubly‐positive charge, many excited states are found to be metastable, four of them (11∏g, 11∏u, 13∑−g, and 11Δg ) having potential wells from 1.52 eV (11∏u) to 2.83 eV (13∑−g). Relative to the ground state configuration, the metastable states arise from the excitations σu→σg(3∑+u), σu→πu(3,1∏g), σ2u→σgπu(3,1∏u), and σ2u→π2u(3∑−g, 1Δg, 1∑+g); they are analogous to those states showing deep local minima in B2 and B+2. Differences in stabilities among quasibound states can be explained on the basis of the asymptotic ΔE’s between repulsive channels B++B+ and appropriate higher‐lying limits (states) B+B2+ of bonding character; another important factor governing stability is the actual bonding character of the electronic configurations assigned to each state. The vertical double‐ionization potential B2→B2+2(π2u→∞) between both ground states is 27.97 eV, the repulsive X1∑+g dication state being created with 8.37 eV excess energy relative to B++B+. Doubly‐ionized states with a chance of being detected because of their long lifetimes against predissociation are those showing a strongly quasibound character, such as (with the vertical double ionization potential in eV given in parentheses): 11∏g(σuπu→∞; 30.29); 11∏u(σ2uπu→σg∞; 31.30); 13∑−g(σ2u→∞; 31.33), and 11Δg(σ2u→∞; 31.95).

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