TOWARD AN ACCURATE DATABASE FOR THE 12 μm REGION OF THE ETHANE SPECTRUM

摘要

The v_9 fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window in the thermal infrared and is commonly used to determine ethane's abundance in the atmospheres of the Jovian planets and comets and to determine their temperature. Precise and accurate absolute intensities of this band are crucial for correct interpretation of recent Cassini observations of ethane spectra in the atmospheres of Saturn and Titan, as well as of Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) observations in the terrestrial atmosphere. Using a spectrum of the v_9 band of ethane recorded at 278 K at the Pacific Northwest National Laboratory, we show that the line parameters available in the HITRAN and GEISA databases do not allow reproduction of the experimental data to within their accuracy. In fact, the integrated band intensity calculated at 296 K using both line lists are, respectively, a factor 1.57 larger and 1.44 smaller than the observed value. Using results from a recent global analysis of data involving the four lowest vibrational states of ethane and measurements of pressure-broadening parameters, we generate a new set of line parameters which we show to provide a much more accurate description of the experimental spectrum of C_2H_6 in the 12 μm region.