Laser flash photolysis of chlorine dioxide: formation and ultraviolet absorption spectrum of chlorine oxide (Cl_2O_3)

The kinetics of ClO_2 photodecomposition in trichlorofluoromethane solutions induced by 337.1-nm pulses were investigated under various experimental conditions. Instantaneous photochemical bleaching is followed by a slower bleaching which follows pseudo-first-order kinetics and leads to the formation of a long-lived transient species absorbing up to 330 nm with λ_(max) ~ 280 nm. At high concentrations of ClO_2 identical amounts of chlorine dioxide are consumed in both stages, revealing that the latter involves stoichiometric reaction of an initially formed intermediate with excess ClO_2 Addition of tetramethylethylene, a very efficient oxygen atom quencher, had no detectable effect on the kinetics of ClO_2 decay. The intermediate is therefore identified as ClO and the new species as Cl_2O_3, chlorine sesquioxide, formed by reaction 5: ClO + ClO_2 → Cl_2O_3.