CL2 PHOTOSENSITIZED DECOMPOSITION OF O3 - REACTIONS OF CLO AND OCLO WITH O3

Cl2 was photolyzed in the temperature range 254 - 296 K with 366 nm radiation in the presence of O3· O3 was removed with quantum yields of 5.8 ± 0.5, 4.0 ± 0.3, 2.9 ± 0.3 and 1.9 ± 0.2 at 24, 10,0 and-21 °C respectively, independent of the initial O3 or Cl2 removal quantum yields were 0.11 ± 0.2 at 24 °C for Cl2 conversions of about 30%, much higher than expected from mass balance considerations based on the initial quantum yield of 0.089 ± 0.013 for OClO formation at 24 °C. The final chlorine-containing product was Cl2O7 which was observed. It was produced at least in part through the formation of OClO as an intermediate which was also observed with an initial quantum yield of Φi[;OClO]; = 2.5 × 103 exp [;-(3025 ± 625)/T]; independent of [O3] or Ia. The results are consistent with the reaction sequence {A figure is presented}. The relative importance of the channels for reaction (2) at 296 K are the following: k2a/k2 = 0.63; k2b/k2 = 0.34; k2c/k2 = 0.0032. Also, k2c/k2b = 2.5 × 103 exp [;-(3025 ± 625)/T];. The upper limit for the rate coefficient was found to be less than 1 × 10-18 cm3 s-1 for channels (24a) and (4b): {A figure is presented}. The addition of nitrogen had no effect, but oxygen reduced -Φ[;O3]; for unknown reasons and several possibilities are discussed. At temperatures below 296 K the equilibrium {A figure is presented} becomes apparent. The reaction of OClO with O3 was also studied by direct mixing of OClO and O3 in a quartz vessel in the temperature range 253 - 296 K, and in the Cl2O3 system by monitoring OClO decay in the dark in the temperature range 264 - 296 K: {A figure is presented} The Arrhenius rate coefficient recommended for reaction (5) is {A figure is presented} The low values of k4 and k5 obtained in this study indicate that reactions (4) and (5) are probably not important in atmospheric chemistry. © 1979.