Differential Excitation Cross Section Measurements of O3 by Electron Impact: A Search for Ozone Excited Electronic States

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The PIs propose to conduct a detailed study of the electronic and vibrational structure of O3 by angle-resolved electron scattering spectroscopy. They assert that the electronic states must be better characterized in order to begin a proper assessment of the role of ozone in the chemistry, radiative transfer, and non-local thermodynamic equilibrium (non-LTE) effects in the terrestrial atmosphere. The PIs plan to reproduce the 15-yr-old electron energy loss spectra of Swanson and Celotta, with improved sensitivity, energy resolution, and angular coverage, and to extend the measurements to include determinations of electronic and vibrational excitation cross sections. The Swanson and Celotta result, though pioneering, is marginal in sensitivity and definitive feature assignments; however it remains the only tangible experimental evidence for the energetics of the controversial low-lying metastable states of ozone. The premise is that these states may participate in the O + O2 recombination sequence, and thus could be significant energy carriers in the photochemistry of O3 in the stratosphere, mesosphere, and thermosphere.