9523356 Copeland In this project, the production of nitrous oxide from the reaction of individual excited states (specifically, Herzberg states) of molecular oxygen with molecular nitrogen will be investigated. This reaction could potentially provide an atmospheric source of nitrous oxide. The general understanding of the sink and source terms that determine the atmospheric altitude profile of nitrous oxide is still evolving. Although the major fraction of atmospheric nitrous oxide comes from the soil and from anthropogenic activity, there may also be a stratospheric source. Recent isotopic measurements of stratospheric nitrous oxide suggest that all of it may not be formed on the earth's surface. Laboratory experiments performed by this SRI research group have demonstrated that the removal of the oxygen Herzberg states in collisions with nitrogen is quite rapid, and that at least for the higher vibrational levels of these states, nitrogen is the dominant quencher in the terrestrial atmosphere. The Herzberg states are generated in the upper stratosphere and lower mesosphere by absorption of solar radiation, and in the upper mesosphere and lower thermosphere by oxygen atom recombination. To have a significant impact on the stratospheric nitrous oxide budget, only a very small reaction yield would be required. Laboratory experiments will be performed where oxygen molecules will be excited to a specific vibrational level of one of the three Herzberg states with a UV laser in a closed system containing oxygen and nitrogen. After the mixture is exposed to the resonant light for minutes to hours, the resulting gases will be analyzed for nitrous oxide using the extremely sensitive technique of frequency-modulated diode laser spectroscopy. If no nitrous oxide is detected, an upper limit for its production will be established, eliminating this reaction system from further speculation.
