Theoretical Study of the Reaction of Hydrogen Atoms with Three Pentene Isomers: 2‑Methyl-1-butene, 2‑Methyl-2-butene, and 3‑Methyl-1-butene

This paper presents a comprehensive potential energy surface (PES) for hydrogen atom addition to and abstraction from 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene and the subsequent ß-scission and H atom transfer reactions. Thermochemical parameters for species on the Ċ5H11 potential energy surface (PES) were calculated as a function of temperature (298–2000 K), using a series of isodesmic reactions to determine the formation enthalpies. High-pressure limiting and pressure-dependent rate constants were calculated using Rice–Ramsperger–Kassel–Marcus theory with a one-dimensional master equation. A number of studies have highlighted the fact that C5 intermediate species play a role in polyaromatic hydrocarbon formation and that a fuel’s chemical structure can be key in understanding the intermediate species formed during fuel decomposition. Rate constant recommendations for both Ḣ atom addition to, and H-atom abstraction by Ḣ atoms from, linear and branched alkenes have subsequently been proposed by incorporating our earlier work on 1- and 2-pentene, and these can be used in mechanisms of larger alkenes for which calculations do not exist. The current set of rate constants for the reactions of Ḣ atoms with both linear and branched C5 alkenes, including their chemically activated pathways, are the first available in the literature of any reasonable fidelity for combustion modeling and are important for gasoline mechanisms. Validation of our theoretical results with pyrolysis experiments of 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene at 2 bar in a single pulse shock tube (SPST) were carried out, with satisfactory agreement observed.本研究构建了一套针对2-甲基-1-丁烯（2-methyl-1-butene）、2-甲基-2-丁烯（2-methyl-2-butene）与3-甲基-1-丁烯（3-methyl-1-butene）的氢原子加成与氢抽提反应，以及后续β-裂解（β-scission）和氢原子转移反应的完整势能面（potential energy surface, PES）。针对C₅H₁₁势能面（PES）上的物种，本研究以298~2000 K的温度为变量，通过一系列等键反应（isodesmic reactions）计算其生成焓（formation enthalpies），进而得到各物种的热化学参数。本研究采用一维主方程（master equation）结合Rice-Ramsperger-Kassel-Marcus理论（Rice–Ramsperger–Kassel–Marcus theory），计算得到高压极限速率常数与压力相关速率常数。已有多项研究表明，C5中间物种在多环芳烃（polyaromatic hydrocarbon）生成过程中具有重要作用，而燃料的化学结构是理解燃料分解过程中生成的中间物种的关键所在。结合本团队此前针对1-戊烯与2-戊烯的研究成果，本研究进一步提出了直链与支链烯烃（linear and branched alkenes）的氢原子加成反应及氢原子抽提反应的速率常数推荐方案，该方案可用于尚无计算数据的更大分子烯烃的反应机理研究。当前这套涵盖化学活化路径的氢原子与直链、支链C5烯烃反应速率常数数据集，是学界首次公开的、适用于燃烧模拟且精度合理的同类数据集，对汽油燃烧机理研究具有重要价值。本研究通过单脉冲激波管（single pulse shock tube, SPST）在2 bar压力下开展2-甲基-1-丁烯、2-甲基-2-丁烯与3-甲基-1-丁烯的热解实验，对理论计算结果进行验证，结果显示二者吻合良好。