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

The degradation process of cyclobutanol (cButOH) by hydroxyl radical (OH), under atmospheric conditions, (750 & PLUSMN; 10) Torr of air and (296 & PLUSMN; 2) K, has been studied. The rate coefficient for the title reaction (k(296K) = (7.3 & PLUSMN; 0.6) x 10(-12) cm(3) 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 x 10(-12) cm(3) 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 (Y-P) depend on the environment composition in which the reaction is studied. In the absence of NOx, cyclobutanone (cButanone) was the only identified product, with Y-cButanone = (0.66 & PLUSMN; 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-1propanol (2M2N1P), were also identified as primary reaction products. Under this condition, we were able to determine only the yields of cButanone and THF (Y-cButanone = 0.38 & PLUSMN; 0.05 and Y-THF = 0.28 & PLUSMN; 0.02). A likely reaction mechanism for the observed products is proposed and the atmospheric implications are discussed.