A global frequency analysis of data in the four lowest vibrational states of ethane

The $\nu _{9}$ fundamental band of ethane occurs in the 12 $\mu $m region. It is the strongest band of ethane in a terrestrial window and is commonly used to determine ethane's abundance in the atmospheres of the Jovian planets and comets, and to determine their temperature. The $\nu _{9}+\nu _{4}-\nu _{4 }$ band occurs in the same region; neither can be analyzed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. Precise and accurate absolute intensities of these bands are crucial for correct interpretation of recent Cassini observations of ethane spectra in the atmospheres of Saturn and Titan. Although, our group has carried out a satisfactory frequency analysis of the $\nu _{9}$ fundamental, a complete analysis of $\nu _{9}+\nu _{4}-\nu _{4}$ is hampered due to an interaction with the $\nu _{12}$ fundamental. This fundamental vibration is infrared inactive. It is also very weakly Raman active. To access this vibrational state, we have obtained a high resolution Fourier transform spectrum of the weak $\nu _{12}-\nu _{9}$ band using a Bruker IFS120HR. In this talk, I will describe a global frequency analysis of data including the four lowest vibrational states of ethane.