Quantum chemical study of the primary step of ozone addition at the double bond of ethylene

The mechanism of the primary step of the interaction between ozone and the double bond of ethylene has been investigated by various methods of quantum chemistry (MP2, QCISD, CCSD, MRMP2) and density functional theory (PBE0, OPTX, CPW91, B3PW91, OLYO, B3LYP, BLYP). The kinetics of two reaction pathways, namely, concerted ozone addition via a symmetric transition state (Criegee mechanism) and nonconcerted ozone addition via a biradical transition state (DeMore mechanism) has been calculated. Both mechanisms are describable well in the single-determinant approximation by the QCISD, CCSD, B3LYP, and PBE0 methods and in the multideterminant approximation by the MRMP2 method. The other methods are less suitable for solving this problem. The calculated data demonstrate that the reaction proceeds via both competing pathways. Rate constant values consistent with experimental data and plausible Criegee-to-DeMore rate constant ratios have been obtained. The concerted addition of ozone to ethylene is significantly more rapid than the nonconcerted addition.