Products of the gas‐phase reactions of O(3P) atoms and O3 with α‐pinene and 1,2‐dimethyl‐1‐cyclohexene

Abstract

Products and mechanisms of the gas‐phase reactions of O(3P) atoms and O3 with the cycloalkenes α‐pinene and 1,2‐dimethyl‐1‐cyclohexene have been investigated at 296±2 K and 740 torr total pressure, using gas chromatography and in situ atmospheric pressure ionization tandem mass spectrometry. The O(3P) atom reaction with α‐pinene led to the formation of α‐pinene oxide and two isomeric C10H16O ketones with yields of 0.77±0.06, 0.18±0.03, and 0.06±0.02, respectively. The O(3P) atom reaction with 1,2‐dimethyl‐1‐cyclohexene produced 1,2‐dimethyl‐1‐cyclohexene oxide with a yield of 0.51±0.16. Product studies of the O3 reactions in the presence of cyclohexane as an OH radical scavenger showed the formation of α‐pinene oxide and pinonaldehyde from α‐pinene with yields of 0.021±0.007 and 0.143±0.024, respectively, and the formation of 1,2‐dimethyl‐1‐cyclohexene oxide, 5‐oxohexanal, and 2,7‐octanedione from 1,2‐dimethyl‐1‐cyclohexene with yields of 0.020±0.006, 0.19±0.05, and 0.07±0.02, respectively. No evidence for the formation of O(3P) atoms from either the reactions of α‐pinene or 1,2‐dimethyl‐1‐cyclohexene with O3 was obtained (with estimated O(3P) atom yields of <0.03 and <0.04, respectively), and the formation of the epoxides is attributed to a direct reaction. An OH radical formation yield from the 1,2‐dimethyl‐1‐cyclohexene reaction of 1.02±0.16 was measured using 2‐butanol to scavenge the OH radicals and form 2‐butanone. Experiments to elucidate the formation route(s) to 2,7‐octanedione and pinonaldehyde were carried out, and it is postulated that these carbonyl products are formed from reactions of the thermalized biradicals with water vapor.