CHLORINE PERCHLORATE FORMATION IN THE GAS-PHASE PHOTOLYSIS OF CHLORINE DIOXIDE

OClO/O2/N2 Mixtures were photolyzed in a temperature controlled 4201 reaction chamber at temperatures between 249 and 300 K and total pressures between 0.5 and 1000 mbar. Initial OClO concentrations were in the range (1.7-5.7) . 10(15) molecule/cm3. Reaction mixtures were analyzed in situ via long-path IR absorption using a Fourier-transform spectrometer. In some experiments product spectra were simultaneously monitored in the IR and the UV. Depending on reaction conditions, the product IR spectra were dominated by absorption bands Of Cl2O3 or Cl2O4 or a mixture of both. Evidence is presented for the crucial role of O atoms in the Cl2O4 formation, suggesting either of the two mechanisms: (I) OClO + O + M --> ClO3 + M, ClO3 + ClO + M --> Cl2O4 + M, or (II) OClO + ClO + M --> Cl2O3 + M, Cl2O3 + O + M --> Cl2O4 + M. Both the weak temperature dependence and the strong pressure dependence of the Cl2O4 yield support mechanism (I). In addition, Cl2O6 was detected as a minor product of OClO photolysis under certain reaction conditions, both by its IR and UV absorption.