Energy Trapping in Dications

The energy interaction curves of a number of diatomic and polyatomic dication systems were calculated in order to study their energy‐trapping properties. Generally, the ab initio complete active space multiconfiguration self‐consistent field method was used in an extended valence + polarization basis set, with compact effective potentials replacing the core electrons. The diatomic dications include all ten possible binary combinations of oxygen, sulphur, selenium, and tellurium. O 2 2+ shows the largest exothermicity, measured from equilibrium to the monocation combination asymptote, and highest barrier to dissociation. The calculated equilibrium bond length and harmonic vibrational frequency agree very well with experiment. The O 2 2+ , SO 2+ , SeO 2+ , and TeO 2+ series show progressively decreasing exothermicities but similar barrier heights. The non‐oxides, in contrast, show similar exothermicities but decreasing barriers with increasing size of the atom constituents. These trends are interpreted in terms of both valence bond curve‐crossing and molecular orbital bonding models. The ozone dication, O 3 2+ , is found to have a number of low‐lying singlet and triplet stationary state structures spanning near‐linear to D 3h 2+ symmetries. Although the calculated exothermicity is even larger than for O 2 2+ , the barrier to O 2 + + O + dissociation is predicted to be low in each case. O 2 2+ surrounded by six argon atoms to model an isolating environment shows increased equilibrium O–O bond length, decreased exothermicity, and increased barrier to dissociation, relative to the bare dication. O 2 2+ flanked at each end by a perpendicularly oriented H 2 molecule in a staggered conformation is obstructed from direct conversion to the water dimer dication by a high barrier. However, [(H 2 O) 2 ] 2+ dissociates smoothly from equilibrium to two water monocations with a large exothermicity but a small barrier.