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首页> 美国卫生研究院文献>other >Multigenerational Theoretical Study of Isoprene Peroxy Radical 1–5-Hydrogen Shift Reactions that Regenerate HOx Radicals and Produce Highly Oxidized Molecules
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Multigenerational Theoretical Study of Isoprene Peroxy Radical 1–5-Hydrogen Shift Reactions that Regenerate HOx Radicals and Produce Highly Oxidized Molecules

机译：异戊二烯过氧自由基1–5氢转移反应的多代理论研究该反应可再生HOx自由基并产生高度氧化的分子

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A computational protocol is employed to glean new insight into the kinetics of several 1,5-hydrogen atom (H) shift reactions subsequent to first- and second-generation OH/ O2 additions to isoprene. The M06–2X density functional was initially used with the Nudged Elastic Band (NEB) method to determine the potential energy surface of OH/O2 addition reactions, the 1,5-H shift reactions, and the fragmentation exit channels. The Master Equation Solver for Multi-Energy Well Reactions (MESMER) was applied to determine the rate constants for OH addition and the 1,5-H shifts. M06–2X was capable of quantifying the rate constants of OH addition to the first and second double bonds of isoprene with deviations less than 17% from the experimentally determined values. However, M06–2X underestimated the 1,5-H shift rate constants of second-generation isoprene peroxy radicals. Consequently, MN15, ωB97X-D, and CBS-QB3 methods were employed to compute average barrier heights to first- and second-generation 1,5-H shifts. In the first generation, the rate constants of H abstraction by β-(1,2) and (4,3) isoprene hydroxy-peroxy radicals from the neighboring hydroxyl group are 1.1 × 10−3 and 2.4 × 10−3 s −1 , respectively. These values are determined primarily by the barrier of the H shift reaction and, to a smaller albeit nonnegligible extent, by the stability of the resulting alkoxy radical and the exit barrier leading to C−C bond dissociation. In contrast, the average second-generation rate constant of 1,5-H shifts from H−R−OH sites to the peroxy radical is 1.8 × 10−1 s −1 , with tunneling playing the significant role of increasing this value relative to first-generation 1,5-H shifts. Under low NOx conditions, first-generation isoprene oxidation reactions may recycle HOx at levels ranging from 10 to 30% due in large part to 1,5-H shifts, with the recycling efficiency being sensitive to HO2 concentrations and temperature. HOx recycling is expected to increase to levels beyond 80% in second-generation reactions of oxidized isoprene species because of isoprene epoxydiol (IEPOX) formation and further 1,5-H shifts that are kinetically favorable.
机译：在第一代和第二代OH / O2加入异戊二烯后，采用了一种计算协议来收集关于数个1,5-氢原子（H）转变反应动力学的新见解。 M06–2X密度泛函最初与微动弹性带（NEB）方法一起使用，以确定OH / O2加成反应，1,5-H移位反应和碎片出口通道的势能面。应用多能阱反应的主方程求解器（MESMER）来确定OH加成和1,5-H位移的速率常数。 M06-2X能够量化异戊二烯的第一个和第二个双键中OH加成的速率常数，与实验测定值的偏差小于17％。但是，M06–2X低估了第二代异戊二烯过氧自由基的1,5-H位移速率常数。因此，采用MN15，ωB97X-D和CBS-QB3方法来计算第一代和第二代1,5-H位移的平均势垒高度。在第一代中，由邻近羟基的β-（1,2）和（4,3）异戊二烯羟基过氧自由基提取H的速率常数为1.1×10-3和2.4×10-3 s -1 ， 分别。这些值主要由H转移反应的势垒决定，在较小的范围内（尽管可以忽略不计）由所得烷氧基的稳定性和导致CC键解离的出口势垒确定。相比之下，从H-R-OH位置到过氧自由基的1,5-H平均第二代速率常数为1.8×10-1 s -1，隧道效应相对于增大该值起着重要作用。第一代1,5-H班次在低NOx条件下，第一代异戊二​​烯氧化反应可能会在很大程度上由于1,5-H的变化而使HOx的回收率在10％到30％之间，并且回收效率对HO2浓度和温度敏感。由于异戊二烯环氧二醇（IEPOX）的形成以及动力学上有利的1,5-H移位，预计在氧化异戊二烯物种的第二代反应中，HOx的回收量将增加到80％以上。

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