Formation of hydroxyl and hydroperoxy radicals in the gas-phase ozonolysis of ethene

Ozonolysis of alkenes is thought be a significant source of free radicals (OH and HO2) in the atmosphere. Although studied for many years, the reaction mechanism and the product yields are still very much under discussion. We report measurements of the production of HO2 radicals from the reaction of O3 with ethene using matrix isolation and electron-spin–resonance spectroscopy (MIESR). Formation of OH radicals was established by conversion of OH to HO2 via reaction with CO. The OH yield is 20±2%, the HO2 yield is 39±3%. Our measurements suggest that the Criegee intermediate in the ground state is not a radical.