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首页> 外文期刊>The Journal of Chemical Physics >Nonthermal rate constants for CH4* + X -> CH3 + HX, X = H, O, OH, and O-2
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Nonthermal rate constants for CH4* + X -> CH3 + HX, X = H, O, OH, and O-2

机译：CH4 * + X - > CH3 + HX，X = H，O，OH和O-2的非热速率常数常数

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摘要

Quasiclassical trajectories are used to compute nonthermal rate constants, k*, for abstraction reactions involving highly-excited methane CH4* and the radicals H, O, OH, and O-2. Several temperatures and internal energies of methane, E-vib, are considered, and significant nonthermal rate enhancements for large E-vib are found. Specifically, when CH4* is internally excited close to its dissociation threshold (E-vib approximate to D-0 = 104 kcal/mol), its reactivity with H, O, and OH is shown to be collision-rate-limited and to approach that of comparably-sized radicals, such as CH3, with k* > 10(-10) cm(3) molecule(-1) s(-1). Rate constants this large are more typically associated with barrierless reactions, and at 1000 K, this represents a nonthermal rate enhancement, k*/k, of more than two orders of magnitude relative to thermal rate constants k. We show that large nonthermal rate constants persist even after significant internal cooling, with k*/k > 10 down to E-vib approximate to D-0/4. The competition between collisional cooling and nonthermal reactivity is studied using a simple model, and nonthermal reactions are shown to account for up to 35%-50% of the fate of the products of H + CH3 = CH4* under conditions of practical relevance to combustion. Finally, the accuracy of an effective temperature model for estimating k* from k is quantified. Published under license by AIP Publishing.
机译：拟痉挛的轨迹用于计算非热速率常数，K *，用于涉及高度激发的甲烷CH4 *和基团H，O，OH和O-2的抽象反应。考虑了甲烷，E-VIB的几种温度和内部能量，并且发现了大型E-VIB的显着的非热速率增强。具体地，当CH 4 *在内部激发时接近其解离阈值（E-VIB近似为D-0 = 104kcal / mol）时，其与H，O和OH的反应性被显示为碰撞率限制并接近相当大小的基团，例如CH3，具有K *> 10（-10）cm（3）分子（-1）S（-1）S（-1）。速率常数该大型更通常与障障反应相关，并且在1000 k处，这表示相对于热速率常数k的两个以上数量级的非热速率增强率K * / k。我们表明，即使在显着的内部冷却之后，大型非热速率常数仍然存在，k * / k> 10向上至e-vib近似到D-0/4。使用简单模型研究了碰撞冷却和非热反应性之间的竞争，并且在与燃烧的实际相关条件下，将非热反应显示为H + CH3 = CH4 *的产物的兴奋剂的55％-50％ 。最后，量化了用于估计K *的有效温度模型的准确性。通过AIP发布在许可证下发布。

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