Isomerization and decomposition of a criegee intermediate in the ozonolysis of alkenes: Dynamics using a multireference potential

The isomerization and decomposition dynamics of the simplest Criegee intermediate CH₂OO have been studied by classical trajectory simulations using the multireference ab initio MR-PT2 potential on the fly. A new, accelerated algorithm for dynamics with MR-PT2 was used. For an initial temperature of 300 K, starting from the transition state from CH ₂OO→CH₂O₂, the system reaches the dioxirane structure in around 50 fs, then isomerizes to formic acid (in ca. 2800 fs), and decomposes into CO+H₂O at around 2900 fs. The contributions of different configurations to the multiconfigurational total electronic wave function vary dramatically along the trajectory, with diradical contributions being important for transition states corresponding to H-atom transfers, while being only moderately significant for CH₂OO. The implications for reactions of Criegee intermediates are discussed. Reading the wave function: The isomerization and decomposition dynamics of the simplest Criegee intermediate CH₂OO were studied by classical trajectory simulations using the multireference ab initio MR-T2 potential on the fly (see picture, numbers are bond lengths (Å) and partial charges). The contributions of different configurations to the multiconfigurational total electronic wave function vary dramatically along the trajectories.