Products of the Gas-Phase Reaction of O₃ with Cyclohexene

Products of the gas-phase reactions of O 3 with cyclohexene and cyclohexene- d 10 were investigated in the presence of OH radical scavengers by gas chromatography with flame ionization detection, combined gas chromatography−mass spectrometry, in situ Fourier transform infrared spectroscopy, and in situ atmospheric pressure ionization mass spectrometry (API-MS). Cyclohexane and cyclohexane- d 12 were used as OH radical scavengers in the experiments using API-MS analyses to allow products formed from the O 3 reactions with cyclohexene and cyclohexene- d 10 to be differentiated from those from the reactions of OH radicals with cyclohexane and cyclohexane- d 12 . The gas-phase products observed from the reaction of O 3 with cyclohexene in the presence of an OH radical scavenger were pentanal (23.6 ± 1.8%); OH radicals (54 ± 8%); formic acid (3.5% initial yield); glutaraldehyde [HC(O)CH 2 CH 2 CH 2 CHO]; adipaldehyde [HC(O)CH 2 CH 2 CH 2 CH 2 CHO], a C 6 H 10 O 3 product attributed to the secondary ozonide; a C 5 H 7 O 2 (OOH) product, a molecular weight 130 hydroxydicarbonyl; and a molecular weight 116 carbonyl compound. Yields of pentanal- d 10, OD radicals, and DC(O)OH from the reaction of O 3 with cyclohexene- d 10, of 16.4 ± 1.4%, 50 ± 7%, and 1.6% (initial), respectively, were obtained. Our data indicate that reactions of the Criegee intermediate to form pentanal (plus CO 2 ) and an OH radical plus organic radical coproduct account for 78 ± 9% of the reaction pathways, with the organic radical coproduct reacting to form (in part) glutaraldehyde. Adipaldehyde can be formed from reaction of the thermalized Criegee intermediate (presumably the anti -intermediate) with water vapor. OH (or OD) radical formation yields were also measured from the reactions of O 3 with propene (40 ± 6%), propene- d 6 (27 ± 4%) α-pinene (86 ± 13%), and 2,3-dimethyl-2-butene (107 ± 16%).