CARBONYL PRODUCTS OF THE GAS-PHASE REACTION OF OZONE WITH SYMMETRICALALKENES

The gas phase reaction of ozone with alkenes is of critical importance in atmospheric chemistry. Major uncertainties include the nature and yields of the carbonyl products and the subsequent reactions of the bi radicals. In this study, carbonyl products have been identified and th eir yields measured in experiments involving the gas phase reaction of ozone with the eight symmetrical alkenes ethylene, cis-3-hexene, cis- 4-octene, trans-4-octene, cis-5-decene, trans-5-decene, trans-2,5-dime thyl-3-hexene, and (cis + trans)-3,4-dimethyl-3-hexene in purified air . Sufficient cyclohexane was added to scavenge the hydroxyl radical (O H) in order to minimize the reaction of OH with the alkenes and with t heir carbonyl products. Formation yields (carbonyl formed/ozone reacte d) of primary carbonyls were close to the value of 1.0 that is consist ent with the simple reaction mechanism: O-3 + R(1)R(2)C=CR(1)R(2) --> R(1)COR(2) + (R(1)R(2)COO). Carbonyls other than the primary carbonyl s R(1)COR(2) were identified as products. Their formation is discussed in terms of subsequent reactions of the R(1)R(2)COO biradicals CH3CH2 CHOO, CH3(CH2)(2)CHOO, CH3(CH2)(3)CHOO, (CH3)(2)CHCHOO, and C2H5C(CH3) OO. Similarities and differences are discussed for cis and trans isome rs and for biradical reactions as a function of the nature and number of the substituents. The results are compared to those for the biradic als H2COO, CH3CHOO, and (CH3)(2)COO from simpler symmetrical alkenes a nd contribute to a better understanding of the ozone-alkene reaction u nder atmospheric conditions.