Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, USA.
J Phys Chem A. 2010 Feb 25;114(7):2553-60. doi: 10.1021/jp909052t.
We report the first isomeric-selective study of the dominant isomeric pathway in the OH-initiated oxidation of isoprene in the presence of O2 and NO using the laser photolysis-laser induced fluorescence (LP-LIF) technique. The photolysis of monodeuterated/nondeuterated 2-iodo-2-methylbut-3-en-1-ol results exclusively in the dominant OH-isoprene addition product, providing important insight into the oxidation mechanism. On the basis of kinetic analysis of OH cycling experiments, we have determined the rate constant for O2 addition to the hydroxyalkyl radical to be 1.0(-0.5)+1.7 x 10(-12) cm3 s(-1), and we find a value of 8.1-2.3+3.4 x 10(-12) cm3 s(-1) for the overall reaction rate constant of the resulting hydroxyperoxy radical with NO. We also report the first clear experimental evidence of the (E) form of the delta-hydroxyalkoxy channel through isotopic labeling experiments and quantify its branching ratio to be (10 +/- 3)%. This puts a rigorous upper limit on the branching of the (E)-delta-hydroxyalkoxy radical channel. Since our measured isomeric-selective rate constants for the dominant outer channel in OH-initiated isoprene chemistry are similar to the overall rate constants derived from nonisomeric kinetics, we predict that the remaining outer addition channel will have similar reactivity.
我们报告了在存在 O2 和 NO 的情况下，OH 引发异戊二烯氧化中主要异构选择性途径的首次异构选择性研究，使用激光光解-激光诱导荧光 (LP-LIF) 技术。单氘代/非氘代 2-碘-2-甲基-3-丁烯-1-醇的光解仅导致主要的 OH-异戊二烯加成产物，为氧化机制提供了重要的见解。基于 OH 循环实验的动力学分析，我们确定了 O2 加成到羟烷基自由基的速率常数为 1.0(-0.5)+1.7 x 10(-12) cm3 s(-1)，并且我们发现生成的羟过氧基与 NO 的总反应速率常数的值为 8.1-2.3+3.4 x 10(-12) cm3 s(-1)。我们还通过同位素标记实验报告了 (E) 形式的 delta-羟基烷氧基通道的首次明确实验证据，并将其分支比定量为 (10 +/- 3)%。这为 (E)-delta-羟基烷氧基自由基通道的分支设置了严格的上限。由于我们测量的 OH 引发异戊二烯化学中主要外部通道的异构选择性速率常数与非异构动力学得出的总速率常数相似，因此我们预测剩余的外部加成通道将具有相似的反应性。
