Mechanistic and kinetic insights into the atmospheric degradation of (CH3)3CF and (CH3)3CCl initiated by Cl atom

Abstract

The degradation mechanism, kinetic properties and subsequent transformation of (CH3)3CF and (CH3)3CCl initiated by ·Cl radicals were investigated using density functional theory. The rate constants and branching ratios for the four hydrogen extraction reaction channels were calculated using the canonical variational transition state theory with small curvature tunneling effect correction. The total rate constants of (CH3)3CF and (CH3)3CCl with ·Cl radicals were 1.52 × 10-11 and 2.45 × 10-11 cm3 molecule-1 s−1 at 296 K, which were in good agreement with the available experimental data. Atmospheric lifetimes of (CH3)3CF and (CH3)3CCl were also predicted theoretically. The self-degradation of (CH3)2C·H2CF and (CH3)2C·H2CCl to form 2-methylpropene by removing F or Cl atom was studied. The stable products for the subsequent transformations of (CH3)2C·H2CF and (CH3)2C·H2CCl in the presence of HO2, O2, and NO were the carbonyl compounds. This study helps us to understand the evolution of halogenated alkanes in complex environments.