Anharmonic effect in the hydrogen atom abstraction reaction kinetics of amino radicals and methanol

• Obtained high-precision rate constants and branch ratios for the hydrogen abstraction reactions of methanol by amino radicals. • Found the strong high-frequency anharmonicity in the transition states and its major impact on the kinetics. • Evaluated the uncertainties of different kinetics effects in the reaction rates. The combustion of the ammonia/methanol blends has attracted much attention due to the potential to reduce carbon emissions. Some previous research had pointed out the importance of involving cross-reactions in the combustion simulation of the ammonia/methanol blends, especially the hydrogen abstraction reaction of amino (NH 2 ) radicals and methanol. Therefore, we carried out a detailed kinetics study of the reaction of NH 2 and methanol in a wide temperature range. The potential energy surface was calculated using the high-level W3X-L//M08-HX/MG3S method, and the specific-reaction-parameter (SRP) scaling factors of frequencies were calculated and used to correct the stronger high-frequency anharmonicity in the transition states than the reactants. The canonical variational transition state theory was used to calculate the rate constants over the temperature range of 200–2000 K, with multi-structural torsional anharmonicity correction and the small curvature tunneling approximation (MS-CVT/SCT). The results show that the stronger high-frequency anharmonicity of the transition states significantly affects the barrier height and thereby causes a deviation factor of 17.5 at 200 K and 1.8 at 2000 K in the prediction of the reaction rates on -OH site of CH 3 OH and a deviation factor of 7.5 at 200 K and 1.2 at 2000 K in the branching ratios on -CH 3 site of CH 3 OH in the reaction of CH 3 OH and NH 2 radicals. In addition, the variational effect and the multi-structural torsional anharmonicity cannot be ignored in the reaction of CH 3 OH and NH 2 radicals. These results can also provide references for evaluating the uncertainty in the reaction kinetics calculations of NH 2 radicals with other alcohol fuels.