Global fit analysis including the ν9 + ν4 − ν4 hot band of ethane: Evidence of an interaction with the ν12 fundamental

Abstract

The ν 9 fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window and is commonly used for the identification of ethane in the Jovian planets. The ν 9 + ν 4 − ν 4 band occurs in the same region; neither can be analysed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. We report here two global fit models including data from both of these bands as well as the ν 3 fundamental and the ν 4, 2 ν 4 − ν 4, and 3 ν 4 torsional transitions. The first is restricted to −5 ⩽ KΔ K ⩽ 15 in the hot band and gives an excellent fit to the included data. Three resonant interactions are identified in this fit—a Coriolis interaction with two resonant cases between the ν 9 torsional stack and that of the ground vibrational state (gs) and a resonant Fermi interaction between the ν 3 fundamental and the gs. Hot band lines with KΔ K < −5 are influenced by a fourth perturbation, with a crossing at −11 < KΔ K < −10, which has been attributed to an interaction with the ν 12 fundamental. A second fit, demonstrating a promising treatment of this interaction, is also presented.