Atmospheric degradation mechanisms and kinetics for OH-initiated oxidation of trans-β-ocimene.

The reaction mechanisms for OH-initiated oxidation of trans-β-ocimene (TBO) in the atmosphere have been investigated at the CCSD(T)/6-31 + G(d)//BH&HLYP/6-311++G(d,p) levels of theory. Classical transition state theory (CTST) is used to obtain the rate constants of initial reaction pathways over the temperature range of 220–1000K. The calculated results show that in the initial reaction pathways of TBO with OH radical, the reaction is dominated by OH addition to the double bonds, and H-abstraction pathways can be negligible at low to medium temperature. The total rate constant computed is 4.56 × 10−10 cm3 molecule−1 s−1 at 298 K, which is consistent with the experimental data. The Arrhenius equation of the total rate constants can be fitted as k t o t a l = 2.20 × 10 − 21 T 3.1 e x p (2499.2 / T) in the temperature range of 220–1000 K. In the presence of O2 and NO, the major degradation products of TBO with OH radical are acetone and 4-methyl-3,5-hexadienal, which are in reasonable agreement with the experimental observations. Furthermore, the ozone formation potential of TBO together with the effects of the TBO oxidation products have also been discussed in detail in the paper. [ABSTRACT FROM AUTHOR]