Rate coefficient and mechanism of the OH-initiated degradation of cyclobutanol: A combined experimental and theoretical study

Abstract

The degradation process of cyclobutanol (cButOH) by hydroxyl radical (OH), under atmospheric conditions, (750 ± 10) Torr of air and (296 ± 2) K, has been studied. The rate coefficient for the title reaction (k296K = (7.3 ± 0.6) x 10−12 cm3 molecule−1 s−1) was determined at 296 K by the conventional relative-rate method. Electronic structure calculations with uCCSD(T)/uBHandHLYP/aug-cc-PVDZ were conducted to study the reaction mechanism. The global rate coefficient was also calculated using the transition state theory with tunnelling corrections, obtaining a value of 5.4 × 10−12 cm3 molecule−1 s−1 in agreement with the experimental determination. Additionally, reaction products identification in clean and NOx-contaminated atmospheres was performed for the first time. The identified reaction products and their corresponding yields (YP) depend on the environment composition in which the reaction is studied. In the absence of NOx, cyclobutanone (cButanone) was the only identified product, with YcButanone = (0.66 ± 0.08). In NOx-contaminated atmospheres, in addition to cButanone, tetrahydrofuran (THF), 2-nitro-1-butanol (2N1B), 3-nitro-2-butanol (3N2B) and 2-methyl-2-nitro-1-propanol (2M2N1P), were also identified as primary reaction products. Under this condition, we were able to determine only the yields of cButanone and THF (YcButanone = 0.38 ± 0.05 and YTHF = 0.28 ± 0.02). A likely reaction mechanism for the observed products is proposed and the atmospheric implications are discussed.