Statistical Theory for the Kinetics and Dynamics of Roaming Reactions
Statistical Theory for the Kinetics and Dynamics of Roaming Reactions
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DOI：
10.1021/jp208347j
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发表时间：
2011-12-22
影响因子：
2.9
通讯作者：
Harding, Lawrence B.
中科院分区：
文献类型：
--
作者：
Klippenstein, Stephen J.;Georgievskii, Yuri;Harding, Lawrence B.
我们提出了一个统计理论的漫游路径上的产品支化分数在单分子和双分子反应的影响。该分析采用分为三个不同步骤的分离：（i）在长程/货车德瓦耳斯势区，通过部分分解，（对于单分子反应物）或部分缔合（对于双分子反应物），（ii）漫游步骤，其涉及片段从长程势的一个区域到另一个区域的重新取向，和（iii）提取，加成和/或从长程区域分解以产生最终产物。漫游诱导通道和其他通道之间的分支是从稳态动力学分析中获得的两个（或多个）中间体的长程区域的潜力。漫游引起的产物分支的统计理论说明通过显式比较与降维轨迹模拟的分解H2 CO，CH 3CHO，CH 3 OOH，和CH 3CCH。这些计算采用高精度的分析潜力，从适合广泛的CASPT 2从头计算电子结构计算。过渡态通量的统计理论计算得到的变量反应坐标过渡态理论方法的推广。在每种情况下，在低能量下，统计分析准确地再现了从轨迹模拟中获得的分支。在较高的能量下，例如，在1千卡/摩尔以上，出现越来越大的差异，这显然是由于动力学偏向于初始分子片段的继续分解（对于单分子反应）。总体而言，基于统计理论的动力学分析被发现提供了一个有用的框架，用于解释的因素，确定漫游路径在不同的化学环境中的意义。
We present a statistical theory for the effect of roaming pathways on product branching fractions in both unimolecular and bimolecular reactions. The analysis employs a separation into three distinct steps: (i) the formation of weakly interacting fragments in the long-range/van der Waals region of the potential via either partial decomposition (for unimolecular reactants) or partial association (for bimolecular reactants), (ii) the roaming step, which involves the reorientation of the fragments from one region of the long-range potential to another, and (iii) the abstraction, addition, and/or decomposition from the long-range region to yield final products. The branching between the roaming induced channel(s) and other channels is obtained from a steady-state kinetic analysis for the two (or more) intermediates in the long-range region of the potential. This statistical theory for the roaming-induced product branching is illustrated through explicit comparisons with reduced dimension trajectory simulations for the decompositions of H2CO, CH3CHO, CH3OOH, and CH3CCH. These calculations employ high-accuracy analytic potentials obtained from fits to wide-ranging CASPT2 ab initio electronic structure calculations. The transition-state fluxes for the statistical theory calculations are obtained from generalizations of the variable reaction coordinate transition state theory approach. In each instance, at low energy the statistical analysis accurately reproduces the branching obtained from the trajectory simulations. At higher energies, e.g., above 1 kcal/mol, increasingly large discrepancies arise, apparently due to a dynamical biasing toward continued decomposition of the incipient molecular fragments (for unimolecular reactions). Overall, the statistical theory based kinetic analysis is found to provide a useful framework for interpreting the factors that determine the significance of roaming pathways in varying chemical environments.