OH radical formation yields from the gas‐phase reactions of O₃ with alkenes and monoterpenes

Abstract

The compound 2‐butanol has been used to scavenge ≥95% of the OH radicals formed in the reactions of O 3 with the alkenes 2,3‐dimethyl‐2‐butene and 2‐methyl‐2‐butene and with the monoterpenes α‐pinene and sabinene at 296±2 K and atmospheric pressure of air, with the OH radical formation yields from these O 3 reactions being obtained from the amounts of 2‐butanone formed. The rate constant for the reaction of the OH radical with 2‐butanol was measured using a relative rate method; the rate constant was determined to be (9.2±2.4) × 10 −12 cm 3 molecule −1 s −1 at 296±2 K, where the indicated error includes the estimated overall uncertainties in the rate constant for the reference organic (cyclohexane). The formation yield of 2‐butanone from the reaction of the OH radical with 2‐butanol was determined to be 0.695±0.073. Using this 2‐butanone formation yield from the OH radical reaction with 2‐butanol, the OH radical formation yields from the reactions of O3 with 2,3‐dimethyl‐2‐butene, 2‐methyl‐2‐butene, α‐pinene, and sabinene were determined to be 0.80±0.12, 0.93±0.14, 0.76±0.11, and 0.33±0.06, respectively. These OH radical formation yields agree to within ±25% with the yields previously derived using cyclohexane to scavenge OH radicals and measuring the amounts of cyclohexanone plus cyclohexanol formed. Our present OH radical formation yield for 2,3‐dimethyl‐2‐butene is also in good agreement with the value of 0.7 previously reported from a comprehensive product study.