Higher oxides of chlorine: Absorption cross-sections of Cl₂O₆ and C1₂O₄, the decomposition of Cl₂O₆, and the reactions of OClO with O and O₃

The absorption cross-sections of Cl₂O₆ and Cl₂O₄ have been obtained using a fast flow reactor with a diode array spectrometer (DAS) detection system. The absorption cross-sections at the wavelengths of maximum absorption (λ _max) determined in this study are those of Cl₂O₆: (1.47±0.15) ×10^-17 cm²UP>, at λ_max =276 nm and T=298 K; and Cl₂O₄: (9.0±2.0) ×10^-19 cm² molecule^-1, at λ_max=234 nm and T=298 K. Errors quoted are two standard deviations together with estimates of the systematic error. The shapes of the absorption spectra were obtained over the wavelength range 200-450 nm for Cl₂O₆ and 200-350 nm for Cl₂O₄, and were normalized to the absolute cross-sections obtained at λ _max for each oxide, and are presented at 1 nm intervals. These data are discussed in relation to previous measurements.The reaction of O with OClO has been investigated with the objective of observing transient spectroscopic absorptions. A transient absorption was seen, and the possibility is explored of identifying the species with the elusive sym-ClO₃ or ClO₄, both of which have been characterized in matrices, but not in the gas-phase. The photolysis of OClO was also re-examined, with emphasis being placed on the products of reaction. UV absorptions attributable to one of the isomers of the ClO dimer, chloryl chloride (ClClO₂) were observed; some Cl₂O₄ was also found at long photolysis times, when much of the ClClO₂ had itself been photolysed. We suggest that reports of Cl₂O₆ formation in previous studies could be a consequence of a mistaken identification. At low temperatures, the photolysis of OClO leads to the formation of Cl₂O₃ as a result of the addition of the ClO primary product to OClO.ClClO₂ also appears to be one product of the reaction between O₃ and OClO, especially when the reaction occurs under explosive conditions. We studied the kinetics of the non-explosive process using a stopped-flow technique, and suggest a value for the room-temperature rate coefficient of (4.6±0.9)×10^-19 cm³ molecule^-1 s^-1 (limit quoted is 2 σ random errors).The photochemical and thermal decomposition of Cl₂O₆ is described in this paper. For photolysis at λ=254 nm, the removal of Cl₂O₆ is not accompanied by the build up of any other strong absorber. The implications of the results are either that the photolysis of Cl₂O₆ produces Cl₂ directly, or that the initial photofragments are converted rapidly to Cl₂. In the thermal decomposition of Cl₂O₆, Cl₂O₄ was shown to be a product of reaction, although not necessarily the major one. The kinetics of decomposition were investigated using the stopped-flow technique. Atelatively high [OClO] present in the system, the decay kinetics obeyed a first-order law, with a limiting first-order rate coefficient of 0.002 s^-1.