Atmospheric chemistry of HCFC-133a: The UV absorption spectra of CF₃CClH and CF₃CClHO₂ radicals, reactions of CF₃CClHO₂ with NO and NO₂ and fate of CF₃CClHO radicals

The UV absorption spectra of CF3CClH and CF3CClHO2 radicals have been investigated. The CF3CClH spectrum was quantified over the wavelength range 225-280 nm. The absorption cross section at 250 nm was (139 ± 16) × 10-20 cm2 molecule-1. The absorption spectrum for CF3CClHO2 was quantified over the wavelength range 225-290 nm, and at 250 nm σ250 nm = (258 ± 30) × 10-20 cm2 molecule-1.

The kinetics of the reactions of the peroxy radical CF3CClHO2 with NO and NO2 were studied and the derived rate constants were k3 = (1.0 ± 0.3) × 10-11 cm3 molecule-1 s-1 and k4 = (6.4 ± 1.5) × 10-12 cm3 molecule-1 s-1, respectively. The self-reaction rate for the CF3CClHO2 radicals was measured and a value of k6obs = (4.4 ± 0.3) × 10-12 cm3 molecule-1 s-1 was obtained.

The reactions of F atoms with CF3CH2Cl and of CF3CClH with O2 were found to proceed with rate constants of k8 = (2.0 ± 0.6) × 10-12 cm3 molecule-1 s-1 and k2 = (1.4 ± 0.1) × 10-12 cm3 molecule-1 s-1, respectively. The reaction of CF3CClHO2 radicals with NO gives NO2, and by implication CF3CClHO radicals, which in the atmosphere (a) react with O2 to give CF3C(O)Cl and (b) decompose to give, most likely, CF3 radicals and HC(O)Cl.

In 700 Torr of N2 diluent the rate constant ratio kO2/kdiss = (2.1 ± 0.4) × 10-19 cm3 molecule-1. As part of the present work, relative rate techniques were used to measure rate constants for the reactions of Cl and F atoms with CF3CH2Cl of (6.8 ± 1.2) × 10-15 and (2.1 ± 0.5) × 10-12 cm3 molecule-1 s-1, respectively.

All experiments were performed at 296 ± 2 K.