A kinetic and mechanistic study of the gas-phase reactions of OH radicals and Cl atoms with some halogenated acetones and their atmospheric implications

Abstract

Rate coefficients for the reactions of hydroxyl radicals and chlorine atoms with a series of halogenated acetones of the type CX₃COCH₃ (X = H, Cl, F) have been determined using a photolytic relative-rate technique at T = 298 K and at 760 Torr total pressure. The reactions studied and the rate coefficients obtained are shown in the table.

Reaction Reaction number Rate coefficient/cm³ molecule⁻¹ s⁻¹ OH + CH₃COCH₃ → products (1) (2.2 ± 0.5) × 10⁻¹³ OH + CH₂ClCOCH₃ → products (2) (4.2 ± 0.8) × 10⁻¹³ OH + CHCl₂COCH₃ → products (3) (3.8 ± 0.8) × 10⁻¹³ OH + CCl₃COCH₃ → products (4) (1.5 ± 0.3) × 10⁻¹⁴ OH + CH₂FCOCH₃ → products (5) (2.1 ± 0.4) × 10⁻¹³ OH + CF₃COCH₃ → products (6) (6.9 ± 1.3) × 10⁻¹⁵ Cl + CH₃COCH₃ → products (7) (2.2 ± 0.4) × 10⁻¹² Cl + CH₂ClCOCH₃ → products (8) (2.0 ± 0.2) × 10⁻¹² Cl + CHCl₂COCH₃ → products (9) (1.7 ± 0.3) × 10⁻¹³ Cl + CCl₃COCH₃ → products (10) (1.7 ± 0.3) × 10⁻¹⁴ Cl + CH₂FCOCH₃ → products (11) (8.2 ± 1.6) × 10⁻¹³ Cl + CF₃COCH₃ → products (12) (8.0 ± 1.6) × 10⁻¹⁵

The errors quoted reflect an estimate of the absolute uncertainty in the measured rate coefficients of ±20%. For reactions (7)–(12), Fourier transform infrared spectroscopy was used to identify products. Qualitative ultra-violet absorption spectra were also recorded for most of the halogenated species investigated in this study, and have been used together with the kinetic data to derive atmospheric lifetimes for these species.