Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p21a1334n&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P21A-1334
Physics
0343 Planetary Atmospheres (5210, 5405, 5704), 5405 Atmospheres (0343, 1060), 5410 Composition (1060, 3672), 5464 Remote Sensing, 6281 Titan
Scientific paper
Propane (C3H8) was first detected on Titan by the Voyager 1 IRIS spectrometer in 1980, which identified four stratospheric emission bands (ν21 at 748 cm-1, ν16 at 922 cm-1, ν15 at 1054 cm-1 and ν7 at 1158 cm-1). Subsequent analyzes of this dataset have largely focused on the strongest of these bands (ν21) to infer the VMR (~ 7×10-7 in the stratosphere and relatively uniform with latitude), although it is significantly disadvantaged by being coincident with a strong R-branch line of acetylene. The Composite Infrared Spectrometer (CIRS) onboard Cassini is now providing the most complete infrared mapping of Titan yet obtained. Prior results have included the retrieval of the vertical and latitudinal profiles of minor gas species, including propane, again exclusively via the ν21 band, the only band for which a linelist is publicly available. We present new modeling of CIRS low-latitude limb spectra acquired from 2004 to 2008. The residuals after modeling all gases except propane clearly show all four bands detected by IRIS, now at much higher signal to noise. In addition, we show that four further bands are clearly evident once the emissions of methane (CH4) and ethane (C2H6) have been modeled and subtracted out: ν8 at 869 cm-1, ν14 at 1338 cm-1, ν13 at 1376 cm-1 and ν19 at 1472 cm-1). Using a new line list for the bands in the range 1300 to 1500 cm-1, we model the ν14, ν13 and ν19 emission bands and compare to abundances retrieved using the ν21 at 748 cm-1. This work has several purposes. Firstly, we demonstrate the urgent need for laboratory spectroscopic measurements of the propane bands at 869, 922, 1054 and 1158 cm-1 leading to line strength listings suitable for spectral calculations. Secondly, we show that the current line list for the 748 cm-1 band does not fit the data accurately, and requires a new spectroscopic study. Finally, we discuss the possibility of new gaseous molecular detections in the regions dominated by these ubiquitous propane bands, once they can be properly modeled.
Bezard Bruno
Coustenis Athena
Flasar Michael F.
Flaud J.
Hewagama Tilak
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