Abstract
We present a direct ab initio and hybrid density functional theory dynamics study of the thermal rate constants of the unimolecular decomposition reaction of C~2~H~5~O → CH~2~O + CH~3~ at a high‐pressure limit. MPW1K/6‐31+G(d,p), MP2/6‐31+G(d,p), and MP2(full)/6‐31G(d) 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 multicoefficient and multilevel 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 state theory (μVT) and RRKM theory with the Eckart tunneling correction in the temperature range of 300–2500 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 experimental data. The fitted three‐parameter Arrhenius expression from the μVT/Eckart rate constants in the temperature range 200–2500 K is k = 2.52 × 10^12^T^0.41^e^(−8894.0/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. The calculated results are in good agreement with the available experimental data. © 2004 Wiley Periodicals, Inc. J Comput Chem 2: 218–226, 2003