Laboratory Studies of Oxygen Atom Recombination in Nitrogen at Mesospheric Temperatures

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This award supports laboratory experiments to study the kinetics of the process of oxygen atom recombination in a molecular nitrogen environment and the pathways that lead to excited states of molecular oxygen (O2) at temperatures relevant to the Earth's mesosphere. The project will supply basic physical measurements needed to interpret and model important processes in the upper atmosphere, such as O2 airglow and atmospheric dynamics. In addition to observational and theoretical studies of Aeronomy, this work could benefit research on planetary atmospheres. The project will contribute to the training and research experience of one or more postdoctoral fellows and undergraduate students. The role of collisional relaxation, the temperature-dependent recombination rate coefficient, the dominant energy flow pathways, and the resulting O2 excited state yields will be studied. These measurements are needed for a quantitative understanding and reliable modeling of the atmosphere and its airglow emissions. Knowledge of the details relevant to the production of excited O2 is critical input for the study and modeling of atmospheric composition, energy transfer, airglow, and transport dynamics. The experimental methodology involves the photoinitiation of O-atom recombination in a suitable bath gas by an ultraviolet radiation pulse from an excimer laser. Fluorescence and resonance-enhanced multiphoton ionization (REMPI) techniques are used to monitor the decay of the O-atom population and detect excited O2 molecules, thus providing insight into the relevant removal rate coefficients, energy flow pathways, and yields of the excited O2 states produced following recombination.