Direct ab initio dynamics study of the reaction of C2(A3Π u) with CH4.

The reaction of C2(A3Π u) with CH4 has been investigated over a wide temperature range 200-3,000 K by direct ab initio dynamics method at the BMC-CCSD//BB1K/6-311+G(2d,2p) level of theory. The optimized geometries and frequencies of the stationary points are calculated at the BB1K/6-311+G(2d,2p) level, and then the energy profiles of the reactions are refined using the BMC-CCSD method. The activation barrier height for H-abstraction reaction was calculated to be 4.44 kcal/mol in temperature range (337-605 K), and the electron transfer behavior was also analyzed by quasi-restricted molecular orbital method in detail. The canonical variational transition-state theory (CVT) with the small curvature tunneling (SCT) correction method is used to calculate the rate constants over a wide temperature range 200-3,000 K. The theoretical results shows that variational effect is to some extent large in lower temperature range, and small curvature and tunneling effect play important roles to the H-atom abstraction only at lower temperatures. The CVT/SCT rate constants are in good agreement with the available experimental results. Our theoretical study is expected to provide a direct insight into the reaction mechanism and may be useful for estimating the kinetics of the title reaction over a wide temperature range where no experimental data are available so far. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 [ABSTRACT FROM AUTHOR]