title: Accurate determination of the reaction course in HY2 <−> Y + YH (Y = O, S): detailed analysis of the covalent- to hydrogen-bonding transition.
abstract: The accurate prediction of a bond-breaking/bond-forming reaction course is useful but very difficult. Toward this goal, a cost-effective multireference scheme (A. J. C. Varandas, J. Chem. Theory Comput. 2012, 8, 428) is tested that provides a generalization of the Hartree-Fock plus dispersion model for closed-shell interactions, and hence is based on the popular but largely untested idea of performing single point calculations with a high-level method at stationary points or along paths located using a lower level method. The energetics so calculated for the reaction HO2 <−> O + OH is predicted in excellent agreement with the experimental data, whereas the reaction path shows a scar at the onset of hydrogen-bonding: a weak van der Waals type minimum separated from the deep covalent well by a small barrier, all below the O + OH asymptote. The O-OH long-range interaction potential is also examined and possible implications in reaction dynamics discussed. Corresponding attributes for the reaction HS2 <−> S + SH are predicted, in good agreement with the best theoretical and experimental results. A perspective on the general utility of the approach is presented.
authors.affiliation: Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal. varandas@qtvs1.qui.uc.pt
authors.forename: A J C
authors.initials: AJ
authors.lastname: Varandas