Study discovers formation of Criegee intermediates from photochemical oxidation of alkenes

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Study discovers formation of Criegee intermediates from photochemical oxidation of alkenes

Credit: Atmospheric Environment (2024). DOI: 10.1016/j.atmosenv.2024.120828

Organic peroxy ********* (RO₂) and Criegee intermediates (CI, carbonyl oxides) are key reactive species in atmospheric chemistry and play crucial roles in the formation of secondary organic aerosol (SOA).

Recently, a research group from the Institute of Earth Environment of the ******** Academy of Sciences (IEECAS) investigated the formation mechanisms of Criegee intermediates from the OH-initiated oxidation of ethylene (C₂H₄), propylene (C₃H₆) and 2-methylpropene (2-CH₃-C₃H₅) in the presence of O₂ by using quantum chemical and kinetic modeling methods. The paper is

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in the journal Atmospheric Environment.

They found that the dominant reaction pathway of ***-RO₂· + ·OH was the barrierless formation of ROOOH on the singlet photoelectron spectroscopy (PES), with its decomposition into RO and ***₂ ********* being the lowest-energy pathway. The stability of ROOOH increased with increasing methyl substituents. The trioxide intermediate did not form on the triplet PES. H-abstraction from the –CH_x group, which formed carbonyl oxides, was favorable for ***-RO₂ *********.

For the reactions ***-RO₂· + ***-RO·, the dominant pathway was the barrierless formation of ROOOR on the singlet PES, with dissociation back to the separate reactants being the lowest-energy pathway. The number and position of methyl substituents had a minor impact on the stability of ROOOR.

The barrier and endothermicity for the formation of carbonyl oxides from the self-reaction of ***-RO₂ ********* decreased with increasing methyl substituents. The structures of ***-RO₂ ********* strongly influenced the barrier of carbonyl oxides’ formation.

This study enhances the understanding of the traditional pathways involved in the transformation mechanisms of peroxy ********* and Criegee intermediates. It has implications for improving the accuracy of numerical models and assessing the impact of anthropogenic emissions on SOA formation.

More information:
Long Chen et al, Molecular insights into the formation of Criegee intermediates from β-hydroxyperoxy *********, Atmospheric Environment (2024).

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Study discovers formation of Criegee intermediates from photochemical oxidation of alkenes (2024, November 25)
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#Study #discovers #formation #Criegee #intermediates #photochemical #oxidation #alkenes

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