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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >A two transition state model for radical-molecule reactions: Applications to isomeric branching in the OH-Isoprene reaction
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A two transition state model for radical-molecule reactions: Applications to isomeric branching in the OH-Isoprene reaction

机译：自由基分子反应的两个过渡态模型：在OH-异戊二烯反应中的异构支化中的应用

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A two transition state model is applied to the prediction of the isomeric branching in the addition of hydroxyl radical to isoprene. The outer transition state is treated with phase space theory fitted to long-range transition state theory calculations on an electrostatic potential energy surface. High-level quantum chemical estimates are applied to the treatment of the inner transition state. A one-dimensional master equation based on an analytic reduction from two-dimensions for a particular statistical assumption about the rotational part of the energy transfer kernel is employed in the calculation of the pressure dependence of the addition process. We find that an accurate treatment of the two separate transition state regions, at the energy and angular momentum resolved level, is essential to the prediction of the temperature dependence of the addition rate. The transition from a dominant outer transition state to a dominant inner transition state is shown to occur at about 275 K, with significant effects from both transition states over the 30-500 K temperature range. Modest adjustments in the ab initio predicted inner saddle point energies yield predictions that are in quantitative agreement with the available high-pressure limit experimental observations and qualitative agreement with those in the falloff regime. The theoretically predicted capture rate is reproduced to within 10% by the expression [1.71 x 10(-10)(T/298)(-2.58) exp(-608.6/RT) + 5.47 x 10(-11)(T/298)(-1.78) exp(-97.3/RT); with R = 1.987 and T in K] cm(3) molecule(-1) s(-1) over the 30-500 K range. A 300 K branching ratio of 0.67:0.02:0.02:0.29 was determined for formation of the four possible OH-isoprene adduct isomers 1, 2, 3, and < BO > 4 , respectively, and was found to be relatively insensitive to temperature. An Arrhenius activation energy of -0.77 kcal/mol was determined for the high-pressure addition rate constants around 300 K.
机译：在向异戊二烯添加羟基自由基的过程中，将两个过渡态模型用于预测异构体支化。外相转变状态通过相空间理论进行处理，该相空间理论适用于静电势能表面上的远距离过渡状态理论计算。高级量子化学估计被应用于内部过渡态的处理。在对加成过程的压力依赖性进行计算时，采用一个基于二维分解解析的一维主方程，用于关于能量传递核的旋转部分的特定统计假设。我们发现，在能量和角动量分辨的水平上，对两个单独的过渡态区域进行精确处理，对于预测加料速度对温度的依赖性至关重要。从显性外部过渡态到显性内部过渡态的转变显示为发生在约275 K，在30-500 K的温度范围内，两种过渡态都产生了显着影响。从头开始预测的内鞍点能量的适度调整可得出与可用高压极限实验观察值定量一致，与衰减状态下定量一致的预测。理论上预测的捕获率可以通过表达式[1.71 x 10（-10）（T / 298）（-2.58）exp（-608.6 / RT）+ 5.47 x 10（-11）（T / 298）复制到10％以内）（-1.78）exp（-97.3 / RT）; R = 1.987，且T在30-500 K范围内以K] cm（3）分子（-1）s（-1）表示。确定300 K的支化比为0.67：0.02：0.02：0.29，以分别形成四种可能的OH-异戊二烯加合物异构体1、2、3和 4 ，并且相对而言对温度不敏感。对于300 K附近的高压添加速率常数，确定了-0.77 kcal / mol的Arrhenius活化能。

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