Extracting Accurate Molecular Spectroscopic Parameters From High Resolution IR Laboratory Spectroscopy

We report on our molecular spectroscopy effort to determine frequencies, intensities, shapes and broadening in fundamental and low-lying hot band transitions for molecules of interest to contemporary planetary atmospheric investigations. The laboratory measurements, obtained with the NASA/GSFC Heterodyne Instrument for Planetary Wind and Composition (HIPWAC), are described in a companion paper in this session (see Blass et al.) which also compares our results to those of other researchers (e.g., Vander Auwera et al.). Herein we present the analysis methodology and interpretation of the laboratory measurements. We identified molecular species of significance to current outer-planet missions such as the Cassini Mission to Jupiter, Saturn and Titan: ethane (C2H6), including both normal and primary hot band (i.e., _9 and _9 + _4 _ _4); ethylene (C2H4); and allene (C3H4). The laboratory measurements which are the basis for the results reported herein were obtained at a spectral resolution of 0.00003 cm_1 (_1MHz) at 12 µm. At this spectral resolution, the rotation-vibration transitions measured under laboratory conditions (ambient temperature and _1 Torr pressure) are fully resolved and identified without ambiguity. The principal objective is to provide critical laboratory truth for the interpretation of infrared spectral observations of the Cassini mission, follow on missions to Titan and the outer planets, and in the re-interpretation of mid-IR emission spectra from Voyager IRIS, ISO, and ground based IR data of the outer planets. Resultant line intensities (