Ab initio molecular orbital study of potential energy surface for the reaction of C 2H 3 with H 2 and related reactions

Alexander M. Mebel*, Keiji Morokuma, Ming-Chang Lin

*此作品的通信作者

研究成果: Article同行評審

摘要

The potential energy surface of the reaction C 2H 3+H 2→C 2H 4+H→C 2H 5 has been investigated using various theoretical methods including QCISD(T), CCSD(T), RCCSD(T), Gaussian-2 (G2), and the density-functional B3LYP approach. The reaction of the vinyl radical with molecular hydrogen is shown to take place through the hydrogen atom abstraction channel leading to the formation of C 2H 4+H with the activation energy of 10.4 kcal/mol at all the G2, QCISD(T)/ 6-311+G(3df,2p), and CCSD(T)/6-311+G(3df/,2p) levels. The rate constant, calculated using the variational transition state theory with tunneling correction, k=3.68·10 -20·T 2.48·exp(-3587/T) cm 3 molecule -1 s -1, is in good agreement with the experimental estimates. C 2H 5 cannot be formed directly by inserting C 2H 3 to H 2, but can only be produced by addition of H to C 2H 4, with a barrier of 4.5-4.7 kcal/mol calculated at high levels of theory. In order to match the experimental rate constant, the activation energy needs to be adjusted to 2.8 kcal/mol. Generally, the B3LYP method is found to predict well the geometries and vibrational frequencies of various species. However, it is less reliable for energy calculations than the QCISD(T) and CCSD(T) methods.

原文English
頁(從 - 到)3440-3449
頁數10
期刊The Journal of chemical physics
103
發行號9
DOIs
出版狀態Published - 9月 1995

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