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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Dual-Level Direct Dynamics of the Hydroxyl Radical Reaction with Ethane and Haloethanes: Toward a General Reaction Parameter Method
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Dual-Level Direct Dynamics of the Hydroxyl Radical Reaction with Ethane and Haloethanes: Toward a General Reaction Parameter Method

机译：乙烷和卤代乙烷的羟基自由基反应的双层直接动力学：迈向一般反应参数方法

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摘要

The dynamics of hydroxyl radical reactions with ethane, fluoroethane, and chloroethane have been examined in terms of variational transition state theory augmented with multidimensional semiclassical tunneling corrections. Differences in reactivity for hydrogen abstraction from both the primary and the secondary carbon atoms are examined in terms of energetic and entropic effects on the location of the dynamical bottleneck. Interpolated variational transition state theory is used to calculate reaction rate constants at the [G2(MP2)//MP2/6-31G(d,p)]/SCT level of theory. A vibrational-mode correlation analysis is performed; i.e., the character of the vibrational modes are identified as a function of the reaction coordinate and a statistical diabatic model is used to provide qualitative analysis of a possible vibrational-state specific chemistry for this reaction. A significant enhancement of the reaction rate is predicted for the excitation of the pertinent C-H stretching mode of the reactant hydrocarbon molecule. THe standard PM3 Hamiltonian is reparametrized (via a genetic algorithm) to obtain reliable semiempirical potential energy surfaces for the reaction of ethane with the OH radical. The specific reaction parameters (SRP) so obtained are then used to predict the reaction rate constants for both the fluoroethane and chloroethane abstraction reactions. THe temperature dependence of the rate constants calculated at the [G2(MP2)//MP2/6-31G(d,p)///PM3-SRP]/#mu#OMT level of theory are compared with those of experiment and are found to be in very good agreement. (The computed rate constants differ from experiment by, at most, a factor of 2.5.) We demonstrate that the specific reaction parameters can be used for analogous reactions of the same mechanism, implying a general reaction parameter set (GRP) for related molecules. Perhaps reaction rates for larger hydrocarbons (that are of interest in atmospheric and combustion chemistry) can be obtained reliably at low computational cost.
机译：与变异态过渡理论相关联的多维半经典隧穿校正，已经检验了与乙烷，氟乙烷和氯乙烷发生的羟基自由基反应的动力学。从动力学瓶颈位置的能量和熵效应方面研究了从伯碳原子和仲碳原子中提取氢的反应性差异。插值变化过渡态理论用于计算理论值[G2（MP2）// MP2 / 6-31G（d，p）] / SCT的反应速率常数。进行振动模式相关分析;即，将振动模式的特征识别为反应坐标的函数，并使用统计非绝热模型对该反应可能的振动态特定化学性质进行定性分析。对于反应物烃分子的相关C-H拉伸模式的激发，预计反应速率将显着提高。对标准PM3哈密顿量进行重新参数化（通过遗传算法），以获得可靠的半经验势能面，用于乙烷与OH自由基的反应。然后将如此获得的特定反应参数（SRP）用于预测氟乙烷和氯乙烷提取反应的反应速率常数。将在[G2（MP2）// MP2 / 6-31G（d，p）/// PM3-SRP] /＃mu＃OMT水平上计算出的速率常数的温度依赖性与实验值进行比较，得出发现非常一致。 （计算出的速率常数与实验的差异最大为2.5。）我们证明了特定反应参数可用于相同机理的类似反应，这意味着相关分子具有通用反应参数集（GRP）。也许可以以较低的计算成本可靠地获得较大碳氢化合物的反应速率（在大气和燃烧化学中很重要）。

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