Theoretical kinetics of hydrogen abstraction and addition reactions of 3-hexene by me Ö^(3P) and ĊH₃

H-atom abstraction and addition are the two most important reactions in alkene oxidation. As a complement of our synchronization work of 3-hexene chemistry (Feiyu Yang et al., Kinetics of Hydrogen Abstraction and Addition Reactions of 3-Hexene by ȮH Radicals, J. Phys. Chem. A 2017, 121, 1877–1889), high-accuracy electronic structure calculations (DLPNO–CCSD(T)/CBS) and canonical variational transition state theory are used to predict the rate coefficients of the H-atom abstraction and addition reactions of 3-hexene + ĊH₃/Ḣ/Ö system. Although ĊH₃/Ḣ/Ö are all nonpolar radicals, Ḣ + 3-hexene system shows some unique features. Unlike the 3-hexene + ĊH₃/Ö systems, the potential energy surface of 3-hexene + Ḣ system exhibits a unique “negative well” characteristic, suggesting the energy of the well is higher than its corresponding reactant or product. Analysis shows that the “negative well” characteristic is caused by the relative larger zero-point energies of Van der Waals complex of H + 3-hexene system. Moreover, the evolution of adiabatic ground-state energy shows wells/well-like curves at both reactant and product sides for 3-hexene + ĊH₃ and Ö systems, but only at reactant end for 3-hexene + Ḣ system. Vibrational analysis reveals that for 3-hexene + ĊH₃ and Ö systems, the wells/well-like curves are generated by the C = C double bond stretch motion, while it is generated by the forming H–H single bond stretch motion for 3-hexene + Ḣ system. Branching ratio shows that addition and abstraction dominate at low and high temperatures and the critical temperatures are 478 K, 794 K and 735 K for 3-hexene + ĊH₃, Ḣ and Ö systems, respectively. Rate coefficients with a conservative uncertainty of a factor of 5 are estimated based on similar algorithm of Sun and Law. In addition, analyses on the potential energy surface, minimum energy path, adiabatic ground-state energy and activation free Gibbs energy change are also performed in this work.