Theoretical Study of the Reaction of Ethane with Oxygen Molecules in the Ground Triplet and Singlet Delta States

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• 作者：Alexander S. Sharipov ; Alexander M. Starik
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：August 23, 2012
• 年：2012
• 卷：116
• 期：33
• 页码：8444-8454
• 全文大小：433K
• 年卷期：v.116,no.33(August 23, 2012)
• ISSN：1520-5215

文摘

Quantum chemical calculations are carried out to study the reaction of ethane with molecular oxygen in the ground triplet and singlet delta states. Transition states, intermediates, and possible products of the reaction on the triplet and singlet potential energy surfaces are identified on the basis of the coupled-cluster method. The basis set dependence of coupled-cluster energy values is estimated by the second-order perturbation theory. The values of energy barriers are also refined by using the compound CBS-Q and G3 techniques. It was found that the C₂H₆ + O₂(X³危_g^鈥?/i>) reaction leads to the formation of C₂H₅ and HO₂ products, whereas the C₂H₆ + O₂(a¹螖_g) process produces C₂H₄ and H₂O₂ molecules. The appropriate rate constants of these reaction paths are estimated on the basis of variational and nonvariational transition-state theories assuming tunneling and possible nonadiabatic transitions in the temperature range 500鈥?000 K. The calculations showed that the rate constant of the C₂H₆ + O₂(a¹螖_g) reaction path is much greater than that of the C₂H₆ + O₂(X³危_g^{鈥?/sup>) one. At the same time, the singlet and triplet potential surface intersection is detected that leads to the appearance of the nonadiabatic quenching channel O₂(a1螖_g) + C₂H₆ 鈫?O₂(X 3危_g鈥?/sup>) + C₂H₆. The rate constant of this process is estimated with the use of the Landau鈥揨ener model. It is demonstrated that, in the case of the existence of thermal equilibrium in the distribution of molecules over the electronic states, at low temperatures (T < 1200 K) the main products of the reaction of C₂H₆ with O₂ are C₂H₄ and H₂O₂, rather than C₂H₅ and HO₂. At higher temperature (T > 1200 K) the situation is inverted.}