The D/H ratio in Titan's acetylene from high spectral resolution IRTF/TEXES observations

Abstract

We report observations of deuterated acetylene (C${}_2$HD) at 19.3 $\mu$m (519 cm${}^{-1}$) with the Texas Echelon Cross Echelle Spectrograph on the NASA Infrared Telescope Facility in July 2017. Six individual lines from the Q-branch of the ${\nu }_4$ band were clearly detected with a S/N ratio up to 10. Spectral intervals around 8.0 $\mu$m (745 cm${}^{-1}$) and 13.4 $\mu$m (1247 cm${}^{-1}$) containing acetylene (C${}_2$H${}_2$) and methane (CH${}_4$) lines respectively, were observed during the same run to constrain the disk-averaged C${}_2$H${}_2$ abundance profile and temperature profile. Cassini observations with the Composite Infrared Spectrometer (CIRS) were used to improve the flux calibration and help to constrain the atmospheric model. The measured D/H ratio in acetylene, derived from the C${}_2$HD/C${}_2$H${}_2$ abundance ratio, is (1.22${}_{-0.21}^{+0.27})$ $\times$ 10${}^{-4}$, consistent with that in methane obtained in previous studies. Possible sources of fractionation at different steps of the acetylene photochemistry are investigated.

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Cited by in corpus (1)

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