Ab Initio Thermal Rate Calculations of HO + HO = O(3P) + H2O Reaction and Isotopologues

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 117; no. 13; pp. 2678 - 2686
• Main Authors: Nguyen, Thanh Lam, Stanton, John F.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 04.04.2013
• Subjects: Ab initio calculations; Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Chemistry; Electronic structure of atoms, molecules and their ions: theory; Exact sciences and technology; General and physical chemistry; Physics; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Inorganic free radical; Ambient temperature; Reaction kinetics; Tunnel effect; Theoretical study; Hydroxyl radicals; Combustion; Ab initio calculations; Molecule-molecule reactions; Master equations; High pressure
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp312246q

The forward and reverse reactions, HO + HO ⇌ O(3P) + H2O, which play roles in both combustion and laboratory studies, were theoretically characterized with a master equation approach to compute thermal reaction rate constants at both the low and high pressure limits. Our ab initio k(T) results for the title reaction and two isotopic variants agree very well with experiments (within 15%) over a wide temperature range. The calculated reaction rate shows a distinctly non-Arrhenius behavior and a strong curvature consistent with the experiment. This characteristic behavior is due to effects of positive barrier height and quantum mechanical tunneling. Tunneling is very important and contributes more than 70% of total reaction rate at room temperature. A prereactive complex is also important in the overall reaction scheme.