Theoretical Investigation of the Radical-Radical Reaction of O(P-3) + C2H3 and Comparison with Gas-Phase Crossed-Beam Experiments

Abstract

Herein, we present an ab initio study of the prototypal radical radical reactions of ground-state atomic oxygen [O(P-3)] with the vinyl (C2H3) radical using density functional theory and a complete basis set model. Two distinctive pathways on the lowest doublet potential energy surfaces (PESs) were predicted to be in competition: addition and abstraction. The barrierless addition of O(P-3) to the hydrocarbon radicals leads to energy-rich intermediate formation followed by subsequent isomerization and decomposition to yield various products: CH2CO (ketene) + H, CO + CH3, C2HOH (acetylenol) + H, (CCHOH)-C-3,1 + H, H2O + C2H, (CH2)-C-3,1 + HCO, H2CO (formaldehyde) + CH, C2H2 (acetylene) + OH, and (CCH2)-C-3,1 + OH. The competing but minor H-atom abstraction mechanisms produce C2H2 + OH and (CCH2)-C-1,3 + OH. The optimized structures of the reactants, products, intermediates, and transition states and the reaction mechanisms were obtained on the lowest doublet PESs. The major pathway was predicted to be the formation of CH2CO + H through the low-barrier, single-step cleavages of the addition intermediates. The Levine-Bernstein prior method, statistical surprisal approach, and microcanonical Rice-Ramsperger-Kassel-Marcus theory were applied to deduce the energy distributions of H atoms and OH products and quantitative rate constants. On the basis of the statistical theory and the population analysis, the predicted energy distributions were compared to the kinetic energy release of H and the preferential population of the Pi(A') component of OH products reported in recent gas-phase crossed-beam investigations (Park, M. J.; Jang, S. C.; Choi, J. H. J. Chem. Phys. 2012, 137, 204311), and their kinetic and dynamic characteristics were discussed.