N. Moazzen-Ahmadi

Toward an Accurate Database for the 12 μm Region of the Ethane Spectrum

The ν9 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 ethanes 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 ν9 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 C2H6 in the 12 μm region.

Nonpolar nitrous oxide dimer: Observation of combination bands of (14N2O)2 and (15N2O)2 involving the torsion and antigeared bending modes

Spectra of the nonpolar nitrous oxide dimer in the region of the N(2)O ν(1) fundamental band were observed in a supersonic slit-jet apparatus. The expansion gas was probed using radiation from a quantum cascade or a tunable diode laser, with both lasers employed in a rapid-scan signal averaging mode. Four bands were observed and analyzed: new combination bands involving the intermolecular conrotation of the monomers (A(g) antigeared bend) for ((14)N(2)O)(2) and ((15)N(2)O)(2), the previously reported torsional combination band for ((14)N(2)O)(2) with improved signal-to-noise ratio, and the same torsional combination band for ((15)N(2)O)(2). The resulting frequencies for the intermolecular antigeared mode are 96.0926(1) and 95.4912(1) cm(-1) for ((14)N(2)O)(2) and ((15)N(2)O)(2), respectively. This is the third of the four intermolecular frequencies which has now been measured experimentally, the others being the out-of-plane torsion and the geared bend modes. Our experimental results are in good agreement with two recent high level ab initio theoretical calculations.