Stopped‐flow studies of the mechanisms of ozone–alkene reactions in the gas phase propene and isobutene

The reactions of ozone with propene and isobutene have been studied in the gas phase at 298°K and 530 Pa (4 torr) using a stopped‐flow reactor coupled to a photoionization mass spectrometer. Reactant and product concentrations were followed as a function of reaction time. The major reaction products monitored were CH2O, CH3CHO, CO2, and H2O from the propene reaction, and CH2O, (CH3)2CO, CO2, and H2O from the isobutene reaction. The observations were interpreted on the basis of the Criegee mechanism for ozonolysis in solution: magnified image for which we find kA≈kB.In the gas phase the carbene peroxy radical is postulated to isomerize and decompose into molecular and free‐radical products.