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

B. Bézard; C. A. Nixon; S. Vinatier; E. Lellouch; T. Greathouse; R. Giles; N. A. Lombardo; A. Jolly

doi:10.1016/j.icarus.2024.116221

paper

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

arXiv:2407.20882 · doi:10.1016/j.icarus.2024.116221

Abstract

We report observations of deuterated acetylene (C $_{2}$ HD) at 19.3 $μ$ 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 $ν_{4}$ band were clearly detected with a S/N ratio up to 10. Spectral intervals around 8.0 $μ$ m (745 cm $^{- 1}$ ) and 13.4 $μ$ 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.

References in corpus (1)

On the H $_{2}$ abundance and ortho-to-para ratio in Titan's troposphere