Lakshmanan Sandhiya, Pratihar Subha, Machado Francisco B C, Hase William L
Department of Chemistry and Biochemistry , Texas Tech University , Lubbock , Texas 79409 , United States.
Departamento de Química , Instituto Tecnológico de Aeronáutica , São José dos Campos, São Paulo , Brazil.
J Phys Chem A. 2018 May 31;122(21):4808-4818. doi: 10.1021/acs.jpca.8b01002. Epub 2018 May 14.
The reaction of CH with O is of fundamental importance in combustion, and the reaction is complex as a result of multiple extremely exothermic product channels. In the present study, direct dynamics simulations were performed to study the reaction on both the singlet and triplet potential energy surfaces (PESs). The simulations were performed at the UM06/6-311++G(d,p) level of theory. Trajectories were calculated at a temperature of 300 K, and all reactive trajectories proceeded through the carbonyl oxide Criegee intermediate, CHOO, on both the singlet and triplet PESs. The triplet surface leads to only one product channel, HCO + O(P), while the singlet surface leads to eight product channels with their relative importance as CO + HO > CO + OH + H ∼ HCO + O(D) > HCO + OH ∼ CO + H ∼ CO + H + O(D) > CO + H + H > HCO + O(D) + H. The reaction on the singlet PES is barrierless, consistent with experiment, and the total rate constant on the singlet surface is (0.93 ± 0.22) × 10 cm molecule s in comparison to the recommended experimental rate constant of 3.3 × 10 cm molecule s. The simulation product yields for the singlet PES are compared with experiment, and the most significant differences are for H, CO, and HO. The reaction on the triplet surface is also barrierless, inconsistent with experiment. A discussion is given of the need for future calculations to address (1) the barrier on the triplet PES for CH + O → CHOO, (2) the temperature dependence of the CH + O reaction rate constant and product branching ratios, and (3) the possible non-RRKM dynamics of the CHOO Criegee intermediate.
CH与O的反应在燃烧过程中至关重要，由于存在多个极放热的产物通道，该反应较为复杂。在本研究中，进行了直接动力学模拟，以研究单重态和三重态势能面（PESs）上的反应。模拟在UM06/6 - 311++G(d,p)理论水平下进行。在300 K的温度下计算轨迹，并且所有反应轨迹在单重态和三重态PESs上均通过羰基氧化物Criegee中间体CHOO。三重态表面仅导致一个产物通道HCO + O(P)，而单重态表面导致八个产物通道，其相对重要性为CO + HO > CO + OH + H ∼ HCO + O(D) > HCO + OH ∼ CO + H ∼ CO + H + O(D) > CO + H + H > HCO + O(D) + H。单重态PES上的反应无势垒，与实验结果一致，单重态表面的总速率常数为(0.93 ± 0.22) × 10 cm³ molecule⁻¹ s⁻¹，而推荐的实验速率常数为3.3 × 10 cm³ molecule⁻¹ s⁻¹。将单重态PES的模拟产物产率与实验进行比较，最显著的差异在于H、CO和HO。三重态表面上的反应也无势垒，这与实验结果不一致。讨论了未来计算需要解决的问题：(1) CH + O → CHOO在三重态PES上的势垒；(2) CH + O反应速率常数和产物分支比的温度依赖性；(3) CHOO Criegee中间体可能的非RRKM动力学。
