Department of Chemistry, N.I. Lobachevsky State University of Nizhny Novgorod, National Research University, 23 Gagarin Avenue, Nizhny Novgorod 603950, Russia.
J Phys Chem A. 2012 Oct 25;116(42):10420-34. doi: 10.1021/jp307738p. Epub 2012 Oct 10.
The mechanisms of the initial step in chemical reaction between ozone and ethylene were studied by multireference perturbation theory methods (MRMP2, CASPT2, NEVPT2, and CIPT2) and density functional theory (OPW91, OPBE, and OTPSS functionals). Two possible reaction channels were considered: concerted addition through the symmetric transition state (Criegee mechanism) and stepwise addition by the biradical mechanism (DeMore mechanism). Predicted structures of intermediates and transition states, the energies of elementary steps, and activation barriers were reported. For the rate-determining steps of both mechanisms, the full geometry optimization of stationary points was performed at the CASPT2/cc-pVDZ theory level, and the potential energy surface profiles were constructed at the MRMP2/cc-pVTZ, NEVPT2/cc-pVDZ, and CIPT2/cc-pVDZ theory levels. The rate constants and their ratio for reaction channels calculated for both mechanisms demonstrate that the Criegee mechanism is predominant for this reaction. These results are also in agreement with the experimental data and previous computational results. The structure of DeMore prereactive complex is reported here for the first time at the CCSD(T)/cc-pVTZ and CASPT2/cc-pVDZ levels. Relative stability of the complexes and activation energies were refined by single-point energy calculations at the CCSD(T)-F12/VTZ-F12 level. The IR shifts of ozone bands due to formation of complexes are presented and discussed.
通过多参考微扰理论方法（MRMP2、CASPT2、NEVPT2 和 CIPT2）和密度泛函理论（OPW91、OPBE 和 OTPSS 泛函）研究了臭氧和乙烯化学反应初始步骤的机制。考虑了两种可能的反应通道：通过对称过渡态的协同加成（Criegee 机制）和通过自由基机制的逐步加成（DeMore 机制）。报道了中间体和过渡态的预测结构、基元步骤的能量和活化势垒。对于两种机制的速率决定步骤，在 CASPT2/cc-pVDZ 理论水平上对稳定点进行了完整的几何优化，并在 MRMP2/cc-pVTZ、NEVPT2/cc-pVDZ 和 CIPT2/cc-pVDZ 理论水平上构建了势能面轮廓。为两种机制计算的反应通道的速率常数及其比值表明，对于该反应，Criegee 机制占主导地位。这些结果也与实验数据和先前的计算结果一致。首次在 CCSD(T)/cc-pVTZ 和 CASPT2/cc-pVDZ 水平报道了 DeMore 预反应络合物的结构。通过在 CCSD(T)-F12/VTZ-F12 水平上进行单点能计算，对络合物的相对稳定性和活化能进行了精细调整。给出并讨论了由于形成络合物而导致的臭氧带的 IR 位移。
