Ozonolysis is one of the most common reaction pathways for tropospheric alkenes. Although it is understood that the reaction proceeds through via 1,3-cycloaddition to form a carbonyl and a carbonyl oxide, commonly referred to as a Criegee intermediate (CI), no CIs have ever been directly detected in the ozonolysis of alkenes until now, due to the exothermicity of the O3 + alkene reaction, and the high reactivity of the nascent CIs. We present here the first experimental observation of CH2OO in the gas-phase ozonolysis of ethylene, using Fourier transform microwave spectroscopy and a modified reactant injection nozzle, which combines high reactant concentrations with rapid sampling to maximize the concentration of CH2OO. A number of other product species of the O3 + C2H4 reaction are also detected, including formaldehyde, formic acid, dioxirane, and ethylene ozonide, which can all be attributed to either the unimolecular isomerization of excited CH2OO, or the bimolecular reaction of stabilized CH2OO. These results indicate that this method may be utilized to detect larger CIs in the gas-phase ozonolysis of branched alkenes, which closely mimic those found in biogenic emissions.

Observation of the simplest criegee intermediate, CH2OO, in the gas-phase ozonolysis of ethylene

249th National Meeting (2015)

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