Reaction of Stabilized Criegee Intermediates from Ozonolysis of Limonene with Water: Ab Initio and DFT Study

The mechanism of the chemical reaction of H2O with three stabilized Criegee intermediates (stabCI-OO, stabCI-CH3-OO and stabCIx-OO) produced via the limonene ozonolysis reaction has been investigated using ab initio and DFT (Density Functional Theory) methods. It has been shown that the formation of the hydrogen-bonded complexes is followed by two different reaction pathways, leading to the formation of either OH radicals via water-catalyzed H migration or of α-hydroxy hydroperoxide. Both pathways were found to be essential sources of atmospheric OH radical and H2O2 making a significant contribution to the formation of secondary aerosols in the Earth's atmosphere. The activation energies at the CCSD(T)/6-31G(d) + CF level of theory were found to be in the range of 14.70-21.98 kcal mol-1. The formation of α-hydroxy hydroperoxide for the reaction of stabCIx-OO and H2O with the activation energy of 14.70 kcal mol-1 is identified as the most favorable pathway.