Direct dynamics study on the reaction of acetaldehyde with ozone

The hydrogen abstraction reaction of ozone with acetaldehyde has been studied theoretically over the temperature range 250-2500 K. Two different reactive sites of acetaldehyde molecule, CH₃ and CHO groups have been investigated, and results confirm that the CHO group is a highly reactive site. In this study, the geometries and harmonic vibrational frequencies of all stationary points are calculated at the MPW1K, BHandHLYP, and MPWB1K levels of theory. The minimum energy paths (MEPs) were obtained at the MPW1K/6-31+G(d,p) level of theory. To refine the energies along the MEPs of each channel, single-point energy calculations were performed by a higherlevel energy calculation method (denoted as HL). The rate constants were evaluated based on the MEPs from the HL method in the temperature range 250-2500 K by using the conventional transition state theory (TST), the canonical variational transition state theory (CVT), the microcanonical variational transition state theory (μVT), the CVT coupled with small-curvature tunneling (SCT) correction (CVT/SCT), and the μVT coupled with Eckart tunneling correction (μVT/Eckart). The fitted three-parameter Arrhenius expressions of the calculated CVT/SCT and μVT/ Eckart rate constants of the H abstraction from CHO group are k^CVT/SCT(T) = 4.92 × 10^-27 ·T^3.77 ·e^(-78670/T) and k ^μVT/Eokart(r) = 2.10 × 10^-27 ·T ^3.90 ·e^(-7706.2/T), respectively. The fitted three-parameter Arrhenius expressions of the calculated CVT/SCT and μVT/Eckart rate constants of the H abstraction from CH₃ group are k^CVT/SCT(T)=1.27 · 10^-27 ·T^3.94 ·e^(-14554.1/T) and k^μVT/Eckart(T) = 1.62 × 10^-26 ·T^3.66 ·e^(-15459.8/T), respectively.