A computational study of the radical-radical reaction of O(³P) + C₂H₅ with comparisons to gas-phase kinetics and crossed-beam experiments

We present density functional theory (DFT) and complete basis set (CBS) calculations of the prototypical radical-radical reaction of ground-state atomic oxygen [O(³P)] with ethyl (C₂H₅) radicals. The respective reaction mechanisms and dynamics were investigated on the doublet potential energy surfaces using the DFT metthod and CBS model. In the title reaction, the barrierless addition of O(³P) to C₂H₅ led to the formation of energy-rich intermediates that underwent subsequent isomerization and decomposition to yield various products. The products predicted to be found were: H₂CO + CH₃, CH₃CHO + H, c-CH₂OCH₂ + H, ^1,3CH₃COH + H, ^1,3HCOH + CH₃, CH₂CHOH + H, C₂H₃ + H₂O, and CH₂CH₂ + OH. In particular, unlike previous kinetic results, proposed to proceed only through the direct H-atom abstraction process, two distinctive pathways to the formation of CH₂CH₂ + OH were predicted to be in competition: direct, barrierless H-atom abstraction mechanism versus addition process. The competition was consistent with the recent crossed-beam investigations, and their microscopic dynamic characteristics are discussed at the molecular level.