We report the existence of special features in the bonding of the molecules He2+3and BeH2+2. Their hypersurfaces have only local minima at 0.4 and 5.2 eV below the energies of (H2+21Σ+g+ He) and (BeH2+ 2Σ++ H), respectively. In C2v, symmetry the molecules are bound. Vibrational analysis reveals that symmetry breaking turns the He2+3minimum into a saddle point, and thus the molecule fragments into 2He++ He. By contrast, the BeH2+2minimum is shown to hold up under symmetry breaking. Being the ground state, it can trap energy whose only escape is via multidimensional tunneling. The bonding characteristics of BeH2+2depict a structure of the type Be"2+"...H2. The formation of this "dihydrogen complex" is due to the vacant metal-ion orbitals, something which is verified by additional computations on BeH+2. These results are compared with analogous bonding situations in transition-metal compounds. © 1990.
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