Although 248-nanometer radiation falls 0.12 electron volt short of the energy needed to dissociate O2 large densities of ozone (O3) can be produced from unfocused 248-nanometer KrF excimer laser irradiation of pure O2. The process is initiated in some undefined manner, possibly through weak two-photon O2 dissociation, which results in a small amount of O3 being generated. As soon as any O3 is present, it strongly absorbs the 248-nanometer radiation and dissociates to vibrationally excited ground state O2 (among other products), with a quantum yield of 0.1 to 0.15. During the laser pulse, a portion of these molecules absorb a photon and dissociate, which results in the production of three oxygen atoms for one O3 molecule destroyed. Recombination then converts these atoms to O3, and thus O3 production in the system is autocatalytic. A deficiency exists in current models of O3 photochemistry in the upper stratosphere and mesosphere, in that more O3 iS found than can be explained. A detailed analysis of the system as it applies to the upper atmosphere is not yet possible, but with reasonable assumptions about O2 vibrational distributions resulting from O3 photodissociation and about relaxation rates of vibrationally excited O2 a case can be made for the importance of incuding this mechanism in the models.