Direct measurement of the Criegee intermediate CH₂OO in ozonolysis of ethene

The transient species produced from reactions of unsaturated hydrocarbons with ozone, carbonyl oxides, termed “Criegee intermediates”, play a key role in tropospheric oxidation mechanisms. Direct observation and characterization of Criegee intermediates in ozonolysis in situ were proven difficult in decades of efforts. Here, we report the direct measurement of the simplest Criegee intermediate, CH₂OO, from ozonolysis of ethene by cavity ring-down spectroscopy in a flow cell reactor. The transient CH₂OO is quantified rapidly by near-ultraviolet absorption spectra via its B̃(¹A′) ← X̃(¹A′) transition. Time profiles of CH₂OO produced in ozonolysis under quasi-steady state conditions are observed. These CH₂OO concentration profiles benchmark the modeling of the ethene ozonolysis reaction network and mechanism, allowing for determination of the yield and various kinetic data of CH₂OO.