A theoretical study on the β-C–H fission of ethoxy radical

Abstract

Abstract We present a direct ab initio dynamics study of the thermal gas-phase rate constants of the unimolecular decomposition reaction of C 2 H 5 O → CH 3 CHO + H. Both MPW1K/6-31+G(d,p) and QCISD/6-31+G(d,p) methods were employed to optimize the geometries of all stationary points and to calculate the minimum energy path (MEP). The energies of all the stationary points were refined at a series of multi-coefficient and multi-level methods. Among all methods, the QCISD(T)/aug-cc-pVTZ energies are in good agreement with the available experimental data. The rate constants were evaluated based on the energetics from the QCISD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) level of theory using both microcanonical variational transition (mVT) state theory and canonical variational transition (CVT) state theory with the Eckart tunneling correction in the temperature range of 200–2500 K. The calculated rate constants at the QCISD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) level of theory are in good consistent with the theoretical data from Caralp et al. The fitted Arrhenius expression in the temperature range 200–2500 K is k=1.30×10 9 T 1.42 e (−1.03×10 4 /T) s −1 . The falloff curves of pressure-dependent rate constants are performed using master-equation method within the temperature range of 391–471 K.