A New Laboratory Source of Ozone and Its Potential Atmospheric Implications

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Abstract
Although 248-nanometer radiation falls 0.12 electron volt short of the energy needed to dissociate O 2 , large densities of ozone (O 3 ) can be produced from unfocused 248-nanometer KrF excimer laser irradiation of pure O 2 . The process is initiated in some undefined manner, possibly through weak two-photon O 2 dissociation, which results in a small amount of O 3 being generated. As soon as any O 3 is present, it strongly absorbs the 248-nanometer radiation and dissociates to vibrationally excited ground state O 2 (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 O 3 molecule destroyed. Recombination then converts these atoms to O 3 , and thus O 3 production in the system is autocatalytic. A deficiency exists in current models of O 3 photochemistry in the upper stratosphere and mesosphere, in that more O 3 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 O 2 vibrational distributions resulting from O 3 photodissociation and about relaxation rates of vibrationally excited O 2 , a case can be made for the importance of including this mechanism in the models.

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