Direct ab initio dynamics study of rate constants and kinetic isotope effects for C₂(A³Π_u) + CH₃OH reaction

Abstract

The hydrogen abstraction of CH₃OH by C₂ (A³Π _u ) has been investigated by direct ab initio dynamics over a wide temperature range 200–3000 K. The potential energy surfaces (PESs) have been constructed at the UCCSD(T)/aug-cc-pVTZ//UMP2/6-311++G(d,p) levels of theory. Two different hydrogen abstractions on the methyl and hydroxyl sites of methanol are considered. For the methyl H-abstraction, it is essentially a hydrogen atom transfer (HAT), whereas the hydroxyl site H-abstraction is better described as a proton coupled electron transfer (PCET) according to the Natural Bond Orbital (NBO) analysis. The results suggest that the methyl site reaction is dominant, and the calculated rate constants are roughly consistent with available experimental values. On the other hand, the temperature dependence of deuterium kinetic isotope effects (KIEs) analysis reveals a substantial normal isotope effect in the methyl H-abstraction process, while normal and inverse KIEs coexist in the hydroxyl H-abstraction channel. Furthermore, the three and four–parameter expressions of Arrhenius rate constants are also provided within 200–3000 K.

Keywords:

• C₂
• rate constants
• temperature dependence
• KIE

Acknowledgments

This work is supported by the National Natural Science Foundation of China (NSFC No. 21073075, 21103064, 21173097), Research Fund for the Doctoral Program of Higher Education of China (RFDP No. 20100061110046), the Special Funding of State Key Laboratory of Theoretical and Computational Chemistry, Jilin University and Basic Research Fund of Jilin University (No. 421010061439, 450060445067).