Abstract
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.
Highlights
The stabilized Criegee intermediates from the ozonolysis of alkenes can react with various atmospheric compounds [1,2,3,4,5], with the formaldehyde, H2O, NOx, SO2, H2SO4 and CO and many others
The oxidation of H2O by stabilized Criegee intermediates in ozonolysis of alkenes can contribute to the formation of secondary organic aerosol (SOA) [31,32]
The mechanistic diagrams for the reactions of H2O with three stabilized Criegee intermediates from ozonolysis of limonene are shown in Schemes 2–4, respectively
Summary
The stabilized Criegee intermediates (stabilized carbonyl oxides) from the ozonolysis of alkenes can react with various atmospheric compounds [1,2,3,4,5], with the formaldehyde, H2O, NOx, SO2, H2SO4 and CO and many others. The mechanistic diagrams for the reactions of H2O with three stabilized Criegee intermediates (stabCI-OO, stabCI-CH3-OO and stabCIx-OO) from ozonolysis of limonene are shown in Schemes 2–4, respectively. In the reaction between stabCI-CH3-OO and H2O, the hydrogen-bonded complex M1H2_S evolves via their corresponding transition states (TSM11H2_S and TSM12H2_S), leading to the formation of. The important role of the reaction between Criegee intermediates from ozonolysis of limonene and H2O for the formation of SOA and organic acids affecting both the global climate changes and public health is well established, the mechanism of these reactions remains poorly understood. The reaction of H2O with three more complex stabilized Criegee intermediates (stabCI-OO, stabCI-CH3-OO and stabCIx-OO) from ozonolysis of limonene has been investigated in order to gain new insights of the oxidation mechanisms under atmospheric conditions. A thorough thermochemical analysis has been carried out and its results and implications for the ozonolysis of limonene have been discussed
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