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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Large Nonstatistical Branching Ratio in the Dissociation of Pentane-2,4-dione Radical Cation: An Ab Initio Direct Classical Trajectory Study
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Large Nonstatistical Branching Ratio in the Dissociation of Pentane-2,4-dione Radical Cation: An Ab Initio Direct Classical Trajectory Study

机译：戊烷-2,4-二酮自由基阳离子离解中的大非统计分支比：从头开始直接经典轨迹研究

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The dissociation of pentane-2,4-dione radical cation has been studied by ab initio direct classical trajectory calculations at the MP2/6-31G(d) level of theory. A bond additivity correction has been used to improve the MP2 potential energy surface (BAC-MP2). A microcanonical ensemble was constructed using quasiclassical normal-mode sampling by distributing 10 kcal/mol of excess energy above ZPE for the transition state for the tautomerization of the enol with a terminal double bond, 4-hydroxypent-4-en-2-one radical cation, to the diketo form. A total of 244 trajectories were run starting from this transition state, yielding pentane-2,4-dione radical cation and depositing energy in the terminal CC bond. As a result, the branching ratio for dissociation of the terminal CC bond versus the interior CC bonds is significantly larger than expected from RRKM theory. The branching ratio for the dissociation of the two interior CC bonds is similar to 20: 1, with the one closest to the activated methyl breaking more often. Since the two interior bonds are equivalent and should dissociate with equal probability, this branching ratio represents a very large deviation from statistical behavior. A simple kinetic scheme has been constructed to model the dissociation rates. The nonstatistical behavior is seen because the rate of energy flow within the molecule is comparable to or less than the rates of dissociation for the activated system. In addition to the expected dissociation products, some of the trajectories also lead to the formation of an ester-like product, prop-l-en-2-yl acetate radical cation.
机译：戊烷-2,4-二酮自由基阳离子的解离已通过理论上从头开始的直接经典轨迹计算来研究，其理论值为MP2 / 6-31G（d）。键加和校正已用于改善MP2势能表面（BAC-MP2）。使用准经典的正常模式采样，通过在ZPE上方分配10 kcal / mol的过剩能量用于过渡态，从而使烯醇与末端双键4-羟基戊-4-en-2-一个自由基进行互变异构化，从而构建了微规范集合体。阳离子，以二酮形式存在。从该过渡态开始总共运行了244条轨迹，产生了戊2,4-二酮自由基阳离子，并在末端CC键中沉积了能量。结果，末端CC键与内部CC键解离的支化比显着大于RRKM理论的预期。两个内部CC键解离的支化比与20：1相似，最接近活化甲基的支化比更经常断裂。由于两个内部键是等价的，并且应该以相同的概率解离，因此该分支比表示与统计行为的很大偏差。已经构建了简单的动力学方案来模拟解离速率。之所以可以看到非统计行为，是因为分子内的能量流动速率与激活系统的解离速率相当或更小。除了预期的解离产物外，某些轨迹还导致形成酯样产物乙酸-1-烯-2-基乙酸酯自由基阳离子。

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