Ab Initio Study on Mechanisms and Kinetics for Reaction of NCS with NO

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• 作者：Hui-Lung Chen ; Rongshun Zhu ; Hsin-Tsung Chen ; Han-Jung Li ; Shin-Pon Ju
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：June 19, 2008
• 年：2008
• 卷：112
• 期：24
• 页码：5495 - 5501
• 全文大小：754K
• 年卷期：v.112,no.24(June 19, 2008)
• ISSN：1520-5215

文摘

The mechanisms and kinetics of the reaction of a thiocyanato radical (NCS) with NO were investigated by a high-level ab initio molecular orbital method in conjunction with variational RRKM calculations. The species involved were optimized at the B3LYP/6-311++G(3df,2p) level, and their single-point energies were refined by the CCSD(T)/aug-cc-PVQZ//B3LYP/6-311+G(3df,2p) method. Our calculated results indicate favorable pathways for the formation of several isomers of an NCSNO complex. Formation of OCS + N₂ also is possible, although this pathway involves a substantial energy barrier. The predicted total rate constants, k_total, at a 2 torr He pressure can be represented by the following equations: k_total = 9.74 × 10²⁶T^−13.88 exp(−6.53 (kcal mol⁻¹)/RT) at T = 298−950 K and 1.17 × 10⁻²²T^2.52 exp(−6.86 (kcal mol⁻¹)/RT) at T = 960−3000 K, in units of cm³ molecule⁻¹ s⁻¹, and the predicted values are in good agreement with the experimental results in the temperature range of 298−468 K. The calculated results clearly indicate that the branching ratio for R_M1 in the temperature range of 298−950 K has the largest value (R_M1 accounts for 0.53−0.39). However, in the higher temperature range (960−3000 K), the formation of OCS + N₂ (P5) with branching ratio R_P5 (0.40−0.79) becomes dominant. The rate constants for key individual product channels are provided for different temperature and pressure conditions.