Thermochemical and Kinetics of CH3SH + H Reactions: The Sensitivity of Coupling the Low and High-Level Methodologies

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• 作者：Daniely V. V. Cardoso ; Leonardo A. Cunha ; Rene F. K. Spada ; Corey A. Petty ; Luiz F. A. FerrãoOrlando Roberto-Neto ; Francisco B. C. Machado
• 刊名：Journal of Physical Chemistry A
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：121
• 期：2
• 页码：419-428
• 全文大小：488K
• ISSN：1520-5215

文摘

The reaction system formed by the methanethiol molecule (CH₃SH) and a hydrogen atom was studied via three elementary reactions, two hydrogen abstractions and the C–S bond cleavage (CH₃SH + H → CH₃S + H₂ (R1); → CH₂SH + H₂ (R2); → CH₃ + H₂S (R3)). The stable structures were optimized with various methodologies of the density functional theory and the MP2 method. Two minimum energy paths for each elementary reaction were built using the BB1K and MP2 methodologies, and the electronic properties on the reactants, products, and saddle points were improved with coupled cluster theory with single, double, and connected triple excitations (CCSD(T)) calculations. The sensitivity of coupling the low and high-level methods to calculate the thermochemical and rate constants were analyzed. The thermal rate constants were obtained by means of the improved canonical variational theory (ICVT) and the tunneling corrections were included with the small curvature tunneling (SCT) approach. Our results are in agreement with the previous experimental measurements and the calculated branching ratio for R1:R2:R3 is equal to 0.96:0:0.04, with k_R1 = 9.64 × 10^–13 cm³ molecule^–1 s^–1 at 298 K.