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首页> 外文期刊>Physica Scripta: An International Journal for Experimental and Theoretical Physics >Accurate and approximate thermal rate constants for polyatomic chemical reactions
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Accurate and approximate thermal rate constants for polyatomic chemical reactions

机译：多原子化学反应的准确和近似热速率常数

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摘要

In favourable cases it is possible to calculate thermal rate constants for polyatomic reactions to high accuracy from first principles. Here, we discuss the use of flux correlation functions combined with the multi-configurational time-dependent Hartree (MCTDH) approach to efficiently calculate cumulative reaction probabilities and thermal rate constants for polyatomic chemical reactions. Three isotopic variants of the H-2 + CH3 -> CH4 + H reaction are used to illustrate the theory. There is good agreement with experimental results although the experimental rates generally are larger than the calculated ones, which are believed to be at least as accurate as the experimental rates. Approximations allowing evaluation of the thermal rate constant above 400K are treated. It is also noted that for the treated reactions, transition state theory (TST) gives accurate rate constants above 500 K. TST theory also gives accurate results for kinetic isotope effects in cases where the mass of the transfered atom is unchanged. Due to neglect of tunnelling, TST however fails below 400K if the mass of the transferred atom changes between the isotopic reactions.
机译：在有利的情况下，可以根据第一原理为多原子反应计算出高精度的热速率常数。在这里，我们讨论了通量相关函数与多配置时变哈特里（MCTDH）方法的结合使用，以有效地计算多原子化学反应的累积反应概率和热速率常数。 H-2 + CH3-> CH4 + H反应的三种同位素变体用于说明该理论。尽管实验速率通常大于计算的速率，但与实验结果有很好的一致性，据信实验速率至少与实验速率一样准确。处理允许评估高于400K的热速率常数的近似值。还应注意，对于已处理的反应，过渡态理论（TST）给出了高于500 K的准确速率常数。在转移原子的质量不变的情况下，TST理论也给出了动力学同位素效应的准确结果。由于忽略了隧穿，如果转移的原子质量在同位素反应之间发生变化，则TST在400K以下会失败。

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