Lakshmanan Sandhiya, Pratihar Subha, Hase William L
Department of Chemistry and Biochemistry , Texas Tech University , Lubbock , Texas 79409 , United States.
J Phys Chem A. 2019 May 23;123(20):4360-4369. doi: 10.1021/acs.jpca.9b02656. Epub 2019 May 9.
In a previous work [ Lakshmanan , S. ; J. Phys. Chem. A 2018 , 122 , 4808 - 4818 ], direct dynamics simulations at the M06/6-311++G(d,p) level of theory were reported for CH (XB) + O (X∑) reaction on its ground-state singlet potential energy surface (PES) at 300 K. However, further analyses revealed the simulations are unstable for the CH (XB) + O (X∑) reactants on the ground-state singlet surface and the trajectories reverted to an excited-state singlet surface for the CH (ãA) + O (b∑) reactants. Thus, the dynamics reported previously are for this excited-state singlet PES. The PESs for the CH (XB) + O (X∑) and CH (ãA) + O (b∑) reactants are quite similar, and this provided a means to perform simulations for the CH (XB) + O (X∑) reactants on the ground-state singlet PES at 300 K, which are reported here. The reaction dynamics are quite complex with seven different reaction pathways and nine different products. A consistent set of product yields have not been determined experimentally, but the simulation yields for the H atom, CO, and CO are somewhat lower, higher, and lower respectively, than the recommended values. The yields for the remaining six products agree with experimental values. Product decomposition was included in determining the product yields. The simulation CH + O rate constant at 300 K is only 3.4 times smaller than the recommended value, which may be accommodated if the CH + O → CHO potential energy curve is only 0.75 kcal/mol more attractive at the variational transition state for CH + O → CHO association. The simulation kinetics and dynamics for the CH + O and CH + O reactions are quite similar. Their rate constants are statistically the same, an expected result, since their transition states leading to products have energies lower than that of the reactants and the attractive potential energy curves for CH + O → CHO and CH + O → CHO are nearly identical. The product yields for the CH + O and CH + O reactions are also nearly identical, only differing for the CO yield. The reaction dynamics on both surfaces are predominantly direct, with negligible trapping in potential energy minima, which may be an important contributor to their nearly identical product yields.
在之前的一项工作中[Lakshmanan, S.; J. Phys. Chem. A 2018, 122, 4808 - 4818]，报道了在M06/6 - 311++G(d,p)理论水平下，对CH(XB)+O(X∑)反应在其基态单重态势能面(PES)上于300 K进行的直接动力学模拟。然而，进一步分析表明，对于基态单重态表面上的CH(XB)+O(X∑)反应物，模拟是不稳定的，并且轨迹会回到CH(ãA)+O(b∑)反应物的激发态单重态表面。因此，之前报道的动力学是针对这个激发态单重态PES的。CH(XB)+O(X∑)和CH(ãA)+O(b∑)反应物的PES非常相似，这为在300 K下对基态单重态PES上的CH(XB)+O(X∑)反应物进行模拟提供了一种方法，本文对此进行了报道。反应动力学相当复杂，有七种不同的反应途径和九种不同的产物。尚未通过实验确定一组一致的产物产率，但对于H原子、CO和CO的模拟产率分别比推荐值略低、略高和略低。其余六种产物的产率与实验值相符。在确定产物产率时考虑了产物分解。300 K下模拟的CH + O速率常数仅比推荐值小3.4倍，如果CH + O → CHO势能曲线在CH + O → CHO缔合的变分过渡态处仅比其更具吸引力0.75 kcal/mol，这是可以接受的。CH + O和CH + O反应的模拟动力学和动力学非常相似。它们的速率常数在统计上是相同的，这是一个预期的结果，因为它们导致产物的过渡态能量低于反应物的能量，并且CH + O → CHO和CH + O → CHO的吸引势能曲线几乎相同。CH + O和CH + O反应的产物产率也几乎相同，只是在CO产率上有所不同。两个表面上的反应动力学主要是直接的，在势能极小值处的捕获可忽略不计，这可能是它们产物产率几乎相同的一个重要原因。
