基态和激发态单重态表面上CH <sub>2</sub> + O <sub>2</sub>反应的直接动力学模拟,The Journal of Physical Chemistry A

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基态和激发态单重态表面上CH ₂ + O ₂反应的直接动力学模拟
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2019-04-29 00:00:00 , DOI: 10.1021/acs.jpca.9b02656
Sandhiya Lakshmanan ₁ , Subha Pratihar ₁ , William L. Hase ₁

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在以前的工作中[Lakshmanan，S .； J.物理化学甲 2018， 122，4808-4818]，在M06 / 6-311 ++ G（d，p）的报告为理论值的水平直接动力学模拟³ CH₂（X³乙₁）+³ Ô₂（X³在300 K的基态单重态势能表面（PES）上发生∑_g^–）反应。但是，进一步的分析表明，对于³ CH₂（X³ B₁）+³ O₂（X³ ∑_g），模拟是不稳定的^–基态单线态表面上）的反应物和恢复到激发态的单表面的轨迹¹ CH ₂（ã ¹阿₁）+ ¹ Ö ₂（B ¹ Σ_克⁺）的反应物。因此，先前报道的动力学是针对该激发态单重态PES的。所述的PES为³ CH ₂（X ³乙₁）+ ³ Ô ₂（X ³ Σ_克^-）和¹ CH ₂（ã ¹阿₁）+¹ O ₂（b ¹ ∑ _g⁺）反应物非常相似，这为在地面上进行³ CH ₂（X ³ B ₁）+ ³ O ₂（X ³ ∑ _g^–）反应物的模拟提供了一种方法。状态单线态PES在300 K，此处报告。反应动力学非常复杂，具有七个不同的反应路径和九个不同的产物。尚未通过实验确定一致的一组产品收率，但是模拟了H原子，CO和CO _2的收率分别比建议值低，高和低。其余六种产品的产率与实验值一致。产品分解包括在确定产品产率中。在300 K下的模拟³ CH ₂ + ³ O ₂速率常数仅比建议值小3.4倍，如果³ CH ₂ + ³ O ₂ → ¹ CH ₂ O ₂势能曲线仅为0.75 kcal ，则可以接受该模拟值/ mol在³ CH ₂ + ³的变化跃迁状态下更具吸引力O ₂ → ¹ CH ₂ O ₂缔合。³ CH ₂ + ³ O ₂和¹ CH ₂ + ¹ O ₂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，这是预期的结果，因为导致产物的过渡态能量低于反应物的能量，并且³ CH ₂ + ³ O ₂ → ¹ CH ₂ O _2的势能曲线有吸引力和¹ CH ₂ + ¹ Ò ₂ → ¹ CH ₂ ö ₂几乎相同。³ CH ₂ + ³ O ₂和¹ CH ₂ + ¹ O ₂反应的产物产率也几乎相同，只是CO ₂产率不同。两个表面上的反应动力学主要是直接的，在势能最小值中的捕获可以忽略不计，这可能是它们几乎相同的产物收率的重要贡献者。

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Direct Dynamics Simulations of the CH2 + O2 Reaction on the Ground- and Excited-State Singlet Surfaces

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 ³CH₂ (X³B₁) + ³O₂ (X³∑_g^–) reaction on its ground-state singlet potential energy surface (PES) at 300 K. However, further analyses revealed the simulations are unstable for the ³CH₂ (X³B₁) + ³O₂ (X³∑_g^–) reactants on the ground-state singlet surface and the trajectories reverted to an excited-state singlet surface for the ¹CH₂ (ã¹A₁) + ¹O₂ (b¹∑_g⁺) reactants. Thus, the dynamics reported previously are for this excited-state singlet PES. The PESs for the ³CH₂ (X³B₁) + ³O₂ (X³∑_g^–) and ¹CH₂ (ã¹A₁) + ¹O₂ (b¹∑_g⁺) reactants are quite similar, and this provided a means to perform simulations for the ³CH₂ (X³B₁) + ³O₂ (X³∑_g^–) 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 CO₂ 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 ³CH₂ + ³O₂ rate constant at 300 K is only 3.4 times smaller than the recommended value, which may be accommodated if the ³CH₂ + ³O₂ → ¹CH₂O₂ potential energy curve is only 0.75 kcal/mol more attractive at the variational transition state for ³CH₂ + ³O₂ → ¹CH₂O₂ association. The simulation kinetics and dynamics for the ³CH₂ + ³O₂ and ¹CH₂ + ¹O₂ 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 ³CH₂ + ³O₂ → ¹CH₂O₂ and ¹CH₂ + ¹O₂ → ¹CH₂O₂ are nearly identical. The product yields for the ³CH₂ + ³O₂ and ¹CH₂ + ¹O₂ reactions are also nearly identical, only differing for the CO₂ 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.

更新日期：2019-04-29

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