Ab Initio Kinetics for Hydrogen Abstraction from Aldehydes and Alcohols by CH₃Ȯ Radicals

The process of hydrogen abstraction by methoxy radicals (CH3Ȯ) represents a fundamental reaction class in hydrocarbon combustion chemistry, playing a pivotal role in fuel decomposition kinetics and radical chain propagation mechanisms. The reaction rate constants for hydrogen abstraction from C1–C2 aldehydes and C1–C3 alcohols by CH3Ȯ radicals are systematically studied by using high-level quantum chemical calculations. Geometry optimization, determination of vibrational frequency, and dihedral angle scans are conducted with the M06-2X/6-311++G(d,p) approach. The QCISD(T)/cc-pVXZ (X = D, T) and MP2/cc-pVXZ (X = D, T, and Q) levels of theory are employed for calculating the single-point energies. Rate constants are derived using transition-state theory, which incorporates quantum mechanical effects, while the thermochemical properties are obtained through statistical thermodynamics. Rate comparisons are conducted for abstracting hydrogen from different sites for a given molecule and from a specific site in different molecules. All computational results are subsequently integrated into the NUIGMech1.3 model to evaluate their impact on the prediction of ignition delay times (IDTs). The results indicate that the newly introduced thermodynamic and kinetic parameters have a significant effect on the IDTs of NC3H7OH and IC3H7OH. Sensitivity and flux analyses are conducted to determine the essential reactions that govern the observed phenomena.甲氧基自由基（methoxy radicals，CH3Ȯ）夺取氢的过程是烃类燃烧化学中的一类基础反应，在燃料分解动力学与自由基链传播机制中发挥关键作用。本研究采用高精度量子化学计算方法，系统探究了CH3Ȯ自由基从C1~C2醛及C1~C3醇中夺取氢的反应速率常数。几何优化、振动频率测定与二面角扫描均采用M06-2X/6-311++G(d,p)方法完成。单点能计算则采用QCISD(T)/cc-pVXZ（X=D、T）与MP2/cc-pVXZ（X=D、T、Q）理论级别。反应速率常数通过包含量子力学效应的过渡态理论（transition-state theory）推导得到，热化学性质则通过统计热力学（statistical thermodynamics）方法获取。本研究针对单分子不同位点的氢夺取反应，以及不同分子的特定位点氢夺取反应开展了速率对比分析。所有计算结果随后被整合至NUIGMech1.3模型中，以评估其对点火延迟时间（ignition delay times，IDTs）预测的影响。结果表明，新引入的热力学与动力学参数对正丙醇（NC3H7OH）与异丙醇（IC3H7OH）的点火延迟时间具有显著影响。本研究还开展了敏感性分析与通量分析，以确定支配该观测现象的核心反应。