Several Levels of Theory for Description of Isotope Effects in Ozone: Symmetry Effect and Mass Effect,The Journal of Physical Chemistry A

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Several Levels of Theory for Description of Isotope Effects in Ozone: Symmetry Effect and Mass Effect
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2018-10-31 00:00:00 , DOI: 10.1021/acs.jpca.8b09025
Alexander Teplukhin ₁ , Dmitri Babikov ₁

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The essential components of theory for the description of isotope effects in recombination reaction that forms ozone are presented, including the introduction of three reaction pathways for symmetric and asymmetric isotopomers, a brief review of relevant experimental data for singly- and doubly substituted isotopologues, the definitions of ζ-effect and η-effect, and the introduction of isotopic enrichment δ. Two levels of theory are developed to elucidate the role of molecular symmetry, atomic masses, vibrational zero-point energies, and rotational excitations in the recombination process. The issue of symmetry is not trivial, since the important factors, such as 1/2 and 2, appear in seven different places in the formalism. It is demonstrated that if all these effects are taken into account properly, then no anomalous isotope effects emerge. At the next level of theory, a model is considered in which one scattering resonance (sitting right at the top of centrifugal barrier) is introduced per ro-vibrational channel. It is found that this approach is equivalent to statistical treatment with partition functions at the transition state. Accurate calculations using hyper-spherical coordinates show that no isotope effects come from difference in the number of states. In contrast, differences in vibrational and rotational energies lead to significant isotope effects. However, those effects appear to be local, found for the rather extreme values of rotational quantum numbers. They largely cancel when rate coefficients are computed for the thermal distribution of rotational excitations. Although large isotope effects (observed in experiments) are not reproduced here, this level of theory can be used as a foundation for more detailed computational treatment, with accurate information about resonance energies and lifetimes computed and included.

中文翻译：

臭氧同位素效应描述的几个理论层面：对称效应和质量效应

介绍了描述形成臭氧的重组反应中同位素效应的理论的基本组成部分，包括引入对称和不对称同位素的三种反应途径，简要介绍了单取代和双取代同位素的相关实验数据，定义δ效应和η效应的关系，以及同位素富集δ的引入。发展了两个层次的理论来阐明分子对称，原子质量，振动零点能量和旋转激发在复合过程中的作用。对称性问题并非无关紧要，因为重要因素（例如1/2和2）出现在形式主义的七个不同位置。已证明，如果适当考虑所有这些影响，则不会出现异常同位素影响。在理论的下一个层面，考虑一个模型，其中每个旋转振动通道引入一个散射共振（位于离心屏障的顶部）。发现该方法等效于在过渡状态下使用分区函数进行统计处理。使用超球面坐标进行的精确计算表明，没有同位素效应来自状态数的差异。相反，振动能和旋转能的差异会导致明显的同位素效应。但是，这些效应似乎是局部的，是针对旋转量子数的极高值发现的。当为旋转激励的热分布计算速率系数时，它们会大大抵消。尽管此处未复制大同位素效应（在实验中观察到），

更新日期：2018-10-31

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