Formation of hydroxyl and hydroperoxy radicals in the gas-phase ozonolysisof 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 reactio n mechanism and the product yields are still very much under discussion. We report measurements of the production of HO2 radicals from the reaction of O-3 with ethene using matrix isolation and electron-spin-resonance spectro scopy (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 3 9 +/- 3%. Our measurements suggest that the Criegee intermediate in the gro und state is not a radical. (C) 1999 Elsevier Science B.V. All rights reser ved.