Other
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.4109b&link_type=abstract
American Astronomical Society, DPS meeting #42, #41.09; Bulletin of the American Astronomical Society, Vol. 42, p.1040
Other
Scientific paper
The near infrared bands of methane were the first observed in the outer planets and Titan. With the very long paths of rays within the atmospheres of these objects, scattering, pressure and temperature inhomogeneities are important. The spectrum of methane is very complex and long laboratory gas cells are difficult to cool to outer solar system temperatures. The absorption is usually modeled statistically. Violations of the modeling assumptions cause poor extrapolations of simulations based upon laboratory parameters. These band models generally do not provide transmissions that are multiplicative, so proper modeling of scattering and inhomogeneous atmospheres is not possible.
The Intra Cavity Laser Spectrometer of the University of Missouri, St. Louis obtained low temperature (99-161K), low pressure ( few Torr), long path (few km) and high resolution ( 0.01 cm-1 HWHM) spectra of methane covering the entire 890 nm feature (10925-11500 cm-1), the deepest band below 1.1 µm. At these temperatures fewer spectral lines are visible and the Doppler width is substantially smaller than at room temperature. The result is a dense, but manageable spectrum from which line positions, intensities and lower state energies are derived on a line by line basis by the William and Mary multispectrum nonlinear least squares fitting technique. For temperatures less than 160K, simulation of the spectrum at infinite resolution is possible. Simulations at various physical conditions will be shown and compared to band models and other laboratory spectra.
Support at William and Mary was provided by NASA through grant NNX08AF06G. Support at UM, St. Louis provided by NASA through grant NAG5-12013, from NSF through grant CHE-0213356 and by the University of Missouri Research Board. Partial support at Bridgewater College was provided by its Martin Science Research Institute and from an AAS Small Research Grant.
Benner Chris D.
Coakley James A. Jr.
Dolph Justin D.
Haga Kasie J.
Houck C. P.
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