Dynamics calculations and isotopic effect in O + OH(D)→ O2+ H(D) at low energies

Abstract

The deuterium isotopic effect in the gas-phase reaction O(³P)+ OH(²Π)→ O₂(X³Σ_g^–)+ H(²S) has been studied in detail over the range of translational energies 0.125 ⩽E_tr/kcal mol^–1⩽ 1.0, which correspond to the temperature range 40 ⩽T/K ⩽ 340. State-to-state dynamics calculations covering the range of rotational quantum numbers 0 ⩽j⩽ 14 have been carried out using both the quasi-classical internal energy quantum mechanical threshold (QCT-IEQMT) and quasi-classical rotational and vibrational energy quantum mechanical threshold (QCT-NVEQMT) methods. The QCT-NVEQMT calculations show an inversion of population in the vibrational distributions of the product O₂ molecules, with v′= 1 being the most populated level. It is also found, by both the QCT-IEQMT and QCT-NVEQMT methods, that the initial rotational state of the reactant OH(D) molecule plays an important role in determining non-statistical recrossing. All calculations used the double many-body expansion (DMBE IV) potential-energy surface for ground-state HO₂. The magnitude of the isotopic effect is shown to depend to some extent on the approach used for the dynamics calculations. The contributions of the various terms to the thermal rate coefficient are also examined.