Photolysis of ozone at 693 nm in solid oxygen. Isotopic effects in ozone reformation

The photodissociation of 18O3 (fully substituted ozone or 888) in the visible region has been studied in a natural oxygen matrix at 10 K combining 693 nm laser irradiation with infrared absorption spectroscopy. Ozone 888 is converted to the (unsymmetrical and symmetrical) 668 and 686 species which are further converted to the normal 666 species through the exchange of 18O with 16O atoms. The overall photodissociation of 888 is a first-order process and a reasonably simple model is proposed which reproduces satisfactorily the observed kinetic results. The value of the photolytic kinetic rate constant suggests an increase in the absorption cross section for the visible band with respect to that measured in the gas phase. The experiments suggest an enhanced formation rate of the unsymmetrical 668 species with respect to the symmetrical species 686 during the 18O oxygen atom recombination with the matrix 16O2 molecules.