Kinetics Study of H-Atom Abstractions from NH₃ and H₂NO by CH₃O₂

Understanding the low-temperature chemistry of ammonia (NH₃) and its interaction with hydrocarbon chemistry is a significant challenge in the kinetics of ammonia blended fuel combustion, especially with the growing interest in novel combustion concepts and the increasing use of NH₃ as an energy carrier. Carbon-nitrogen (C–N) interactions play an important role in the combustion characteristic of NH₃ blends with hydrocarbon fuels. In this work, the kinetics of two possible C–N interaction reactions, H-atom abstractions from NH₃ and aminoxyl radical (H₂NO) by methylperoxy radical (CH₃O₂), is investigated. These reaction pathways show some sensitivity to the low-temperature ignition of NH₃/CH₄. However, they have not been considered in any combustion kinetic models so far. Due to the intrinsic multi-reference nature of their transition states, the energy barriers for the two reactions are determined using the CASPT2/aug-cc-pVTZ method with the active space of (7e,7o), and CASPT2/cc-pVDZ method with the active space of (14e,12o), respectively, based on the optimized geometries and rovibrational properties obtained at M06-2X/6-311++G (d,p) level of theory. The rate constants for the two reactions in the temperature range 298.15–2000 K are calculated by using transition state theory. By incorporating these two reaction pathways with our calculated rate constants into a NH₃/CH₄ kinetic model, the predicted low-temperature ignition delay times (IDT) of NH₃/CH₄ mixtures become noticeably shorter.