Reaction Energetics for the Abstraction Process C2H3 + H2 → C2H4 + H

The fundamentally important combustion reaction of vinyl radical with hydrogen has been studied in the laboratory by at least five experimental groups. Herein, the reaction C2H3 + H-2 -> C2H4 + H has been examined using focal-point analysis. Molecular energies were determined from extrapolations to the complete basis-set limit using correlation-consistent basis sets (cc-pVTZ, cc-pVQZ, and cc-pV5Z) and coupled-cluster theory with single and double excitations (CCSD), perturbative triples [CCSD(T)], full triples [CCSDT], and perturbative quadruples [CCSDT(Q)]. Reference geometries were optimized at the all-electron CCSD(T)/cc-pCVQZ level. Computed energies were also corrected for relativistic effects and the Born-Oppenheimer approximation. The activation energy for hydrogen abstraction is predicted to be 9.65 kcal mol(-1), and the overall reaction is predicted to be exothermic by 5.65 kcal mol(-1). Natural resonance theory (NRT) analysis was performed to verify the reaction pathway and describe bond-breaking and bond-forming events along the reaction coordinate.