Theoretically derived mechanisms of HPALD photolysis in isoprene oxidation.
Theoretically derived mechanisms of HPALD photolysis in isoprene oxidation.
复制标题
异戊二烯氧化中 HPALD 光解作用的理论推导机制。
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
J. Peeters
中科院分区：
文献类型：
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作者：
Zhen Liu;V. S. Nguyen;J. Harvey;J. Müller;J. Peeters
在这项工作中，我们确定并理论上量化了HPALDs(氢过氧醛)的两种光解机制，这两种机制是在低/中NOx条件下异戊二烯大气氧化过程中过氧基异构化的结果。作为第一种光解机制，我们证明了一部分初始激发的S1态HPALDs通过近乎无障碍的1，5H位移异构化，速率接近1012HPALDs-1-与∼竞争同样快地穿过T2三重态的系间-形成不稳定的双自由基，自发地排出一个OH(羟基)自由基。第二种机制被证明是通过活化的T2三重态双自由基进行的，该双自由基由S1形成，经历了协同的环闭合和OH-排出，产生了氧杂环型的共产物自由基，该自由基迅速地开环给环氧基。在这两种机制中，副产物自由基随后的化学作用会产生额外的第一代羟基。通过这两种机制--这可能不是唯一的光解途径--的组合HPALD-光解量子产率估计为0.55，OH产生的量子产率为0.9，与HPALD代理上的实验数据相当一致(Wolfe等人，Phys.化学。化学。物理，2012，14,7276-7286)。
In this work we identified and theoretically quantified two photolysis mechanisms of HPALDs (hydroperoxy aldehydes) that result from the isomerization of peroxy radicals in the atmospheric oxidation of isoprene at low/moderate NOx. As a first photolysis mechanism, we show that a fraction of the initially excited S1-state HPALDs isomerizes by a near-barrierless 1,5 H-shift at a rate approaching 1012 s-1 - competing with the ∼equally fast intersystem crossing to the T2 triplet state - forming an unstable biradical that spontaneously expels an OH (hydroxyl) radical. A second mechanism is shown to proceed through the activated T2 triplet biradical - formed from S1 - undergoing a concerted ring-closure and OH-expulsion, yielding an oxiranyl-type co-product radical that quickly ring-opens to enoxy radicals. In both mechanisms, subsequent chemistry of the co-product radicals yields additional first-generation OH. The combined HPALD-photolysis quantum yield by these two mechanisms - which may not be the only photolysis routes - is estimated at 0.55 and the quantum yield of OH generation at 0.9, in fair accordance with experimental data on an HPALD proxy (Wolfe et al., Phys. Chem. Chem. Phys., 2012, 14, 7276-7286).
影响因子：
6.3
作者：
Jenkin, M. E.;Young, J. C.;Rickard, A. R.
通讯作者：
Rickard, A. R.