Understanding the insight into the mechanisms and dynamics of the Cl-initiated oxidation of (CH3)3CC(O)X and the subsequent reactions in the presence of NO and O2 (X = F, Cl, and Br)

Abstract

In this work, the density functional and high-level ab initio theories are adopted to investigate the mechanisms and kinetics of reaction of (CH3)3CC(O)X (X = F, Cl, and Br) with atomic chlorine. Rate coefficients for the reactions of chlorine atom with (CH3)3CC(O)F (k1), (CH3)3CC(O)Cl (k2), and (CH3)3CC(O)Br (k3) are calculated using canonical variational transition state theory coupled with small curvature tunneling method over a wide range of temperatures from 250 to 1000 K. The dynamic calculations are performed by the variational transition state theory with the interpolated single-point energies method at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311++G(d,p) level of theory. Computed rate constant is in good line with the available experimental value. The rate constants for the title reactions are in this order: k1<k2<k3, suggesting that the effect of halogen substitution on the mechanisms and dynamics is different. The subsequent and secondary reactions for the hydrogen abstraction intermediates are studied involving NO and O2 molecules in the atmosphere. The atmospheric lifetime and global warming potential (GWP) of (CH3)3CC(O)X (X = F, Cl, and Br) are estimated, and it shows that (CH3)3CC(O)F have larger GWP value than that of (CH3)3CC(O)Cl and (CH3)3CC(O)Br. Due to the presence of Cl and Br atoms, the environmental impact of (CH3)3CC(O)Cl and (CH3)3CC(O)Br may be given more concerns.