Theoretical Study on Reactions of Alkylperoxy Radicals
Theoretical Study on Reactions of Alkylperoxy Radicals
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烷基过氧自由基反应的理论研究
DOI：
10.1021/acs.jpca.9b01496
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发表时间：
2019
影响因子：
2.9
通讯作者：
Li Xiangyuan
中科院分区：
文献类型：
--
作者：
Xu Yanjiao;Xi Shuanghui;Wang Fan;Li Xiangyuan
我们对乙基+O2、丙基+O2和丁基+O2反应的几何形状、驻点相对能量和反应速率常数进行了理论研究，这些反应是相应烷烃低温氧化中的重要反应。采用乙基 + O2 系统的 CCSD(T)/aug-cc-pVTZ 几何形状作为基准，选择合适的交换相关函数进行几何优化。我们的结果表明，具有 6-311+G(d,p) 的 B3LYP 可以为该系统提供可靠的结构，并且其他两个系统的结构都是用该泛函确定的。通过将其结果与乙基 + O2 系统的 CCSD(T)/aug-cc-pVQZ 的结果进行比较，评估显式相关的 CCSD(T)-F12a 和局部相关的 DLPNO-CCSD(T) 方法在势垒高度和反应能量方面的性能。我们的结果表明，使用 cc-pVDZ-F12 基组的 CCSD(T)-F12a 可以实现该系统的可靠能量差，并且该方法可用于计算其他两个系统的单点能量。采用单参考运动方程自旋翻转耦合簇法获得了无势垒反应C2H5·+O2→CH3CH2OO·的势能面，并与破缺密度泛函理论和莫尔斯势的结果进行了比较。这些方法的能量差异<1.6 kcal/mol，但在温度 <500 K 时，速率常数的差异可能相当大，并且本工作中获得的速率常数仅在温度 >500 K 时可靠。这些反应的压力相关速率常数是使用 Rice-Ramsperger-Kassel-Marcus/Master 方程方法确定的。所获得的反应能量、势垒高度和速率常数对于大烷烃自由基和O2之间的反应很有价值，这对于煤油和汽油等燃料的低温燃烧很重要。
We carried out a theoretical study on geometries, relative energies of stationary points, and reaction rate constants for ethyl + O2, propyl + O2, and butyl + O2reactions, which are important reactions in the low-temperature oxidation of corresponding alkanes. Geometries with CCSD(T)/aug-cc-pVTZ for the ethyl + O2system are adopted as the benchmark to choose a proper exchange-correlation functional for geometry optimization. Our results show that B3LYP with 6-311+G(d,p) can provide reliable structures for this system, and structures of the other two systems are determined with this functional. The performances of the explicitly correlated CCSD(T)-F12a and the locally correlated DLPNO-CCSD(T) methods on barrier heights and reaction energies are evaluated by comparing their results with those of CCSD(T)/aug-cc-pVQZ for the ethyl + O2system. Our results indicate that reliable energy differences for this system are achieved with CCSD(T)-F12a using the cc-pVDZ-F12 basis set, and this method is employed in calculating single-point energies for the other two systems. The single-reference equation-of-motion spin-flip coupled-cluster method is adopted to obtain the potential energy surface of the barrierless reaction C2H5· + O2→ CH3CH2OO·, and the results are compared with those using broken-symmetry density functional theory and the Morse potential. Differences between energies with these methods are <1.6 kcal/mol, but the difference in the rate constants could be sizable at temperatures <500 K, and rate constants obtained in this work are reliable only for temperatures >500 K. Pressure-dependent rate constants for these reactions are determined using the Rice–Ramsperger–Kassel–Marcus/Master equation method. The obtained reaction energies, barrier heights, and rate constants could be valuable for reactions between the large alkane radical and O2, which are important in the low-temperature combustion of fuels such as kerosene and gasoline.