Abstract
The syn-CH3CHOO Criegee intermediate formed from the ozonolysis of propene and (E)-2-butene was detected via unimolecular decomposition and subsequent detection of OH radicals by a LIF-FAGE instrument. An observed time dependent OH concentration profile was analysed using a detailed model focusing on the speciated chemistry of Criegee intermediates based on the recent literature. The absolute OH concentration was found to depend on the steady state concentration of syn-CH3CHOO at the injection point while the time dependence of the OH concentration profile was influenced by the sum of the rates of unimolecular decomposition of syn-CH3CHOO and wall loss. By varying the most relevant parameters influencing the SCI chemistry in the model and based on the temporal OH concentration profile, the unimolecular decomposition rate k (293 K) of syn-CH3CHOO was shown to lie within the range 3-30 s(-1), where a value of 20 ± 10 s(-1) yields the best agreement with the CI chemistry literature.
Highlights
Criegee intermediates (CI, carbonyl oxides) are key intermediates in the atmospheric ozonolysis of unsaturated compounds
Chemically activated CH2OO will mostly decompose, as the internal energy is distributed across only a few degrees of freedom, leading to very fast unimolecular reactions, while larger CI such as those obtained from terpenoid ozonolysis will mostly stabilise at 1 atm
CI can isomerise by ring closure, forming a dioxirane that in turn re-isomerizes to an ester or an acid; for small alkenes these latter compounds will receive enough internal energy to immediately decompose forming CO2, OH, CO, HO2, H2O and alkyl fragments
Summary
Criegee intermediates (CI, carbonyl oxides) are key intermediates in the atmospheric ozonolysis of unsaturated compounds. The fate of the Criegee intermediate depends on its nascent energy content, which we broadly divide in two populations:[4,5,6] thermally stabilized and chemically activated. The chemically activated Criegee intermediate has a high energy content and a comparatively short lifetime. It will decompose through the vinyl hydroperoxide (VHP) or ester channels discussed below, though depending on the reaction rates at the given energy and the rate of energy loss in collisions with the bath gas, it can form a stabilised Criegee intermediate (SCI).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
