PRODUCTS OF THE GAS-PHASE REACTIONS OF O(P-3) ATOMS AND O-3 WITH ALPHA-PINENE AND 1,2-DIMETHYL-1-CYCLOHEXENE

Products and mechanisms of the gas-phase reactions of O(P-3) atoms and O-3 with the cycloalkenes alpha-pinene and 1,2-dimethyl-1-cyclohexene have been investigated at 296 +/- 2 K and 740 torr total pressure, us ing gas chromatography and in situ atmospheric pressure ionization tan dem mass spectrometry. The O(P-3) atom reaction with alpha-pinene led to the formation of alpha-pinene oxide and two isomeric C10H16O ketone s with yields of 0.77 +/- 0.06, 0.18 +/- 0.03, and 0.06 +/- 0.02, resp ectively. The O(P-3) atom reaction with 1,2-dimethyl-1-cyclohexene pro duced 1,2-dimethyl-1-cyclohexene oxide with a yield of 0.51 +/- 0.16. Product studies of the O-3 reactions in the presence of cyclohexane as an OH radical scavenger showed the formation of alpha-pinene oxide an d pinonaldehyde from alpha-pinene with yields of 0.021 +/- 0.007 and 0 .143 +/- 0.024, respectively, and the formation of 1,2-dimethyl-1-cycl ohexene oxide, 5-oxohexanal, and 2,7-octanedione from 1,2-dimethyl-1-c yclohexene with yields of 0.020 +/- 0.006, 0.19 +/- 0.05, and 0.07 +/- 0.02, respectively. No evidence for the formation of O(P-3) atoms fro m either the reactions of alpha-pinene or 1,2-dimethyl-1-cyclohexene w ith O-3 was obtained (with estimated O(P-3) atom yields of <0.03 and < 0.04, respectively), and the formation of the epoxides is attributed t o a direct reaction. An OH radical formation yield from the 1,2-dimeth yl-1-cyclohexene reaction of 1.02 +/- 0.16 was measured using 2-butano l to scavenge the OH radicals and form 2-butanone. Experiments to eluc idate the formation route(s) to 2,7-octanedione and pinonaldehyde were carried out, and it is postulated that these carbonyl products are fo rmed from reactions of the thermalized biradicals with water vapor.