最新量子化学与可变反应配位过渡态理论相结合解决H2S + Cl体系的疑难问题
State-of-the-Art Quantum Chemistry Meets Variable Reaction Coordinate Transition State Theory to Solve the Puzzling Case of the H2S + Cl System
摘要：
本文重新研究了H $_2$ S与Cl的大气反应，以检验是否如前所述，由于强烈的再交叉效应和过渡态理论的变分扩展的崩溃，只有明确的动力学计算才能得到反应速率的准确估计。为此，相应的势能面已被彻底研究，从而导致所有驻点的准确表征，其能量已被计算在最先进的状态。为此，耦合团簇理论，包括高达四重激发，连同外推到完整的基组极限，并结合核心价相关，自旋轨道，标量相对论效应以及对角玻恩-奥本海默修正。这种高精度的复合方案也已被更便宜但有前途的计算方法所验证。移动到动力学，变分过渡态理论和它的可变反应坐标扩展的无势垒步骤已被利用，从而获得反应速率常数（8.16 × 10 $^{-11}$ cm $^3$分子$^{-1}$ s $^{-1}$在300 K和1大气压）在显着的协议与实验对应。因此，与前面的权利要求相反，只要进行足够精确的量子化学计算，就不需要援引过渡态理论的任何失败。对H $_2$ S + Cl系统这一令人困惑的案例的研究，使我们能够提出一种强有力的方法来揭示大气和天体物理学感兴趣的反应的热化学和动力学。
英文摘要：
The atmospheric reaction of H$_2$S with Cl has been reinvestigated to check if, as previously suggested, only explicit dynamical computations can lead to an accurate evaluation of the reaction rate because of strong recrossing effects and the breakdown of the variational extension of transition state theory. For this reason, the corresponding potential energy surface has been thoroughly investigated, thus leading to an accurate characterization of all stationary points, whose energetics has been computed at the state of the art. To this end, coupled-cluster theory including up to quadruple excitations has been employed, together with the extrapolation to the complete basis set limit and also incorporating core-valence correlation, spin-orbit, and scalar relativistic effects as well as diagonal Born-Oppenheimer corrections. This highly accurate composite scheme has also been paralleled by less expensive yet promising computational approaches. Moving to kinetics, variational transition state theory and its variable reaction coordinate extension for barrierless steps have been exploited, thus obtaining a reaction rate constant (8.16 x 10$^{-11}$ cm$^3$ molecule$^{-1}$ s$^{-1}$ at 300 K and 1 atm) in remarkable agreement with the experimental counterpart. Therefore, contrary to previous claims, there is no need to invoke any failure of the transition state theory, provided that sufficiently accurate quantum-chemical computations are performed. The investigation of the puzzling case of the H$_2$S + Cl system allowed us to present a robust approach for disclosing the thermochemistry and kinetics of reactions of atmospheric and astrophysical interest.
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