Theoretical studies of anharmonic effect analysis about the hydrogen abstraction reactions on <i>n</i>-heptane in combustion

The hydrogen evolution reaction of n-heptane is an important reaction of n-heptane combustion. The existing theoretical research on the n-heptane hydrogen evolution reaction has low accuracy; the anharmonic effect and tunneling effect are not considered, so the obtained kinetic and thermodynamic parameters cannot meet current engineering requirements. In the present study, hydrogen abstraction reactions on n-heptane by CH3, H, HO2, O, and OH were conducted, while other bimolecular reactions of n-heptane with H are also considered, and the effects of tunneling and the anharmonic effect on the rate coefficients were evaluated. The transition state theory and Yao-Lin method are employed to determine these kinetic and thermodynamic parameters in the reaction system. The results indicate that all hydrogen abstraction reactions of n-heptane are low energy exothermic reactions, while other bimolecular reactions of n-heptane with H are high energy exothermic reactions. Remarkably, the harmonic rate constant of all reactions is always higher than the anharmonic one, and the disparity between the harmonic rate constant and the anharmonic rate constant widens with the increasing temperature. Meanwhile, the influence of the tunneling effect on the reaction rate is significant, and significant negative temperature coefficient behavior was observed in certain reactions.