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[36.06] VUV Absorption Cross Sections of C₂H₂ in the Pressence of Pressure-Induced Effects

R. Wu, F. Chen (University of Southern California)

Significant pressure effects on the absorption band contours, spectral positions, and shapes of Rydberg transitions are well known. The electronic states of C₂H₂ in the VUV and FUV regions include valence and Rydberg states. Thus, in this spectral region very different pressure effects on the absorption features are expected. Pressure effects could have significant impact in modeling the C₂H₂ abundance in the upper atmospheres of Jupiter, Saturn, Neptune, Uranus (H₂ is the predominate atmospheric gas in these giant planets) and Titan¡¦s (N₂ is the predominate gas in this satellite¡¦s atmosphere). It appears necessary to consider high pressure effects in models as our observational capability reaches a new height. The currently research work may provide the data required to interpret the expected Cassini data. We have previously studied the absorption spectrum of C₂H₂ in the presence of H₂ and N₂ to demonstrate the possible pressure effects observable using 0.006 nm resolution. In the present work we have measured H₂ broadening coefficients (full width at half maximum), which are 2.1x10{-5} nm/Torr and 1.02x10{-4} nm/Torr for the respective 150.19 nm and 148.9 nm bands at pressures up to 1000 Torr and at room temperature. The corresponding absorption cross section measurements of C₂H₂ have also been determined. The detailed experimental results will be presented. This research is based on work supported by the NASA Planetary Atmospheres Program under Grant NAG5-11042.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.