Molecular Nitrogen Photoabsorption Cross Section Measurements and Models in Support of Analyses of Planetary Atmospheres

Details Molecular Nitrogen Photoabsorption Cross Section Measurements and Models in Support of Analyses of Planetary Atmospheres Molecular Nitrogen Photoabsorption Cross Section Measurements and Models in Support of Analyses of Planetary Atmospheres

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.6219s&link_type=abstract

American Astronomical Society, DPS meeting #38, #62.19; Bulletin of the American Astronomical Society, Vol. 38, p.609

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The analyses of existing and planned vacuum ultraviolet occultation measurements of the N2-rich atmospheres of Titan, Triton, and Pluto require reliable photoabsorption cross sections for the approximately 100 bands of N2 in the 80 to 100 nm wavelength region. We report measurements of fundamental parameters of the absorption spectrum of 14N2 along with the development of a new, physically-based, quantum-mechanical model for N2 photoabsorption and photodissociation. Advantages of the model include simultaneous computation of the total photodissociation cross section and the branching ratios for dissociation into all energetically-accessible channels, and a seamless treatment of isotopic and temperature effects.
Within individual bands, our measurements indicate significant departures from the predicted line strength distributions based on isolated band models. Line width analyses within each band indicate that predissociation-broadening is often highly dependent on the rotational quantum number. Our coupled Schrödinger equations model of the N2 spectrum, optimized to our laboratory spectra, reproduces these effects and predicts significant band shape asymmetries not predicted by isolated band models. These effects may have a significant bearing on the penetration of solar radiation into nitrogen-rich planetary atmospheres and the consequent photochemistry, including isotopic fractionation. Applications of the model in the vacuum ultraviolet are of particular relevance to the current encounter of Cassini-Huygens with Titan and initial results have been supplied to the UVIS team for solar-occultation analyses.
We gratefully acknowledge funding support from NASA grant NNG05GA03G and from ARC grant DP0558962.

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