Ab initio calculations at the level of CBS-QB3 theory have been performed to investigate the potential energy surface for the reaction of benzyl radical with molecular oxygen. The reaction is shown to proceed with an exothermic barrierless addition of O2 to the benzyl radical to form benzylperoxy radical (2). The benzylperoxy radical was found to have three dissociation channels, giving benzaldehyde (4) and OH radical through the four-centered transition states (channel B), giving benzyl hydroperoxide (5) through the six-centered transition states (channel C), and giving O_2-adduct (8) through the four-centered transition states (channel D), in addition to the backward reaction forming benzyl radical and O2 (channel E). The master equation analysis suggested that the rate constant for the backward reaction (E) of C6H5CH2OO -> C6H5CH2 + O2 was several orders of magnitude higher that those for the product dissociation channels (B- D) for temperatures 300-1500 K and pressures 0.1 - 10 atm; therefore, it was also suggested that the dissociation of benzylperoxy radicals proceeded with the partial equilibrium between the benzyl + O2 and benzylperoxy radicals. The rate constants for product channels B-D were also calculated, and it was found that the rate constant for each dissociation reaction pathway was higher in the order of channel D > channel C > channel B for all temperature and pressure ranges. The rate constants for the reaction of benzyl + O2 were computed from the equilibrium constant and from the predicted rate constant for the backward reaction (E). Finally, the product branching ratios forming CH20 molecules and OH radicals formed by the reaction of benzyl + O2 were also calculated using the stationary state approximation for each reaction intermediate.
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机译：已经进行了CBS-QB3理论级别的从头算计算，以研究苄基与分子氧反应的势能面。已显示该反应是通过将O2无放热地加至苄基进行反应而形成苄基过氧自由基（2）。发现苄基过氧自由基具有三个解离通道，通过四个中心过渡态（通道B）产生苯甲醛（4）和OH自由基，通过六个中心过渡态（通道C）产生氢过氧化苄基（5），并且除了形成苄基和O2的反向反应（通道E）外，还通过四个中心过渡态（通道D）得到O_2加合物（8）。主方程分析表明，在温度为300-1500 K和压力为0.1的情况下，C6H5CH2OO-> C6H5CH2 + O2的向后反应（E）的速率常数比产物离解通道（B-D）的速率常数高几个数量级。 -10个大气压;因此，还建议苄基过氧自由基的离解以苄基+ O 2与苄基过氧自由基之间的部分平衡进行。还计算了产物通道B-D的速率常数，发现在所有温度和压力范围内，每个解离反应路径的速率常数都以通道D>通道C>通道B的顺序更高。由平衡常数和由向后反应（E）的预测速率常数计算出苄基+ O 2反应的速率常数。最后，还使用每个反应中间体的稳态近似值，计算了形成CH20分子的产物支化比和由苄基+ O2反应形成的OH自由基。
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