Accurate Determination of the Reaction Course in HY2 ⇌ Y + YH (Y = O, S): Detailed Analysis of the Covalent- to Hydrogen-Bonding Transition

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2013-08, Vol.117 (32), p.7393-7407
• Main Author: Varandas, A. J. C
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Electronic structure of atoms, molecules and their ions: theory; Exact sciences and technology; Physics
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp401384d

The accurate prediction of a bond-breaking/bond-forming reaction course is useful but very difficult. Toward this goal, a cost-effective multireference scheme ( Varandas A. J. C. , 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.