Photodissociation of NO2 in the region 458–630 nm

Abstract
Measurements on the photodissociation of NO2 into NO+O2 at wavelengths from 457.9 to 630 nm are shown to be consistent with the reaction NO2* +NO2→2NO+O2. The extent of dissociation is determined by measuring the O2 pressure produced during photolysis with high intensity laser irradiation. The quenching of the photodissociation is determined for the inert gases CO2 and Xe. The energy dependence of the rate coefficient of the above reaction is fitted to an RRK model, which indicates the contribution of a very small number of degrees of freedom (?3) so that it is possibly the energy distribution within a single NO2*, rather than an activated complex, which is important in determining the dissociation. A composite of our data with that of others demonstrates the existence of another dissociative mechanism in the region 430–400 nm. The variation of the rate coefficient with energy of this dissociation of NO2* into NO+O is fitted with a model of activation in many degrees of freedom.