Products of the gas-phase reactions of 03 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 03 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)CH2CH2CH2CHO]; adipaldehyde [HC(O)CH2CH2CH2CH2CHO], a C6H10O3 product attributed to the secondary ozonide; a C5H7O2(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 CO2) 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%) alpha-pinene (86 +/- 13%), and 2,3-dimethyl-2-butene (107 +/- 16%).