Atmospheric chemistry of FCO_x radicals: UV spectra and self-reaction kinetics of FCO and FC(O)O₂ and kinetics of some reactions of FCO_x with O₂, O₃, and NO at 296 K

A pulse radiolysis technique has been used to measure the UV spectra of FCO and FC(O)O2 radicals over the ranges 265-275 and 220-290 nm, respectively. At 269.6 nm, σFCO = (1.7 ± 0.2) × 10-18 cm2 molecule-1; at 250 nm, σFC(O)O2 = (2.1 ± 0.2) × 10-18 cm2 molecule-1. The decay of UV absorption was used to study the kinetics of the self-reactions of FCO and FC(O)O2 radicals at 296 ± 2 K.

Observed self-reaction rate constants, defined as -d[FCO]/dt = 2k7[FCO]2 and -d[FC(O)O2]/dt = 2k8obs[FC(O)O2]2, were k7 = (1.6 ± 0.2) × 10-11 and k8obs = (6.0 ± 0.7) × 10-12 cm3 molecule-1 s-1. A rate constant, k1 = (1.2 ± 0.2) × 10-12 cm3 molecule-1 s-1, was derived for the addition reaction FCO + O2 → FC(O)O2 in 1000 mbar of SF6 diluent.

Rate constants for the reactions of FCO, FC(O)O, and FC(O)O2 radicals with NO were determined to be (1.0 ± 0.2) × 10-12, (1.3 ± 0.7) × 10-10, and (2.5 ± 0.8) × 10-11, cm3 molecule-1 s-1, respectively. An upper limit of k3 < 6 × 10-14 cm3 molecule-1 s-1 was measured for the reaction of FC(O)O radicals with O3.

Finally, a rate constant of (5.5 ± 0.7) × 10-12 cm3 molecule-1 s-1 was measured for the association reaction of F atoms to NO in 1000 mbar of SF6 diluent. All experiments were performed at 296 ± 2 K. Results are discussed with respect to the atmospheric chemistry of hydrofluorocarbons.