Titan

The D/H Ratio in Titan’s Acetylene From High Spectral Resolution IRTF/TEXES Observations

By Keith Cowing

Status Report

astro-ph.EP

July 31, 2024

Filed under acetylene, astro-ph.EP, astrochemistry, atmosphere, biochemistry, Cassini, NASA InfraRed Telescope Facility, organic chemistry, Photochemistry, spectrometer, Spectroscopy, Titan

The D/H Ratio in Titan’s Acetylene From High Spectral Resolution IRTF/TEXES Observations — Contribution functions at selected wavenumbers calculated for the best-fitting models (Fig. 5) of CIRS (red lines) and TEXES (blue lines) observations. These contribution functions, which have been normalized at each wavenumber, are Jacobians that give the rate of change of spectral flux with temperature (Panel A), logarithm of C2H2 mole fraction (Panel B), and logarithm of C2HD mole fraction (Panel C). — astro-ph.EP

We report observations of deuterated acetylene (C₂HD) at 19.3 μm (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 ν4 band were clearly detected with a S/N ratio up to 10. Spectral intervals around 8.0 μm (745 cm⁻¹) and 13.4 μm (1247 cm⁻¹) containing acetylene (C₂H₂) and methane (CH₄) lines respectively, were observed during the same run to constrain the disk-averaged C₂H₂ 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 C₂HD/C₂H₂ abundance ratio, is (1.22+0.27−0.21) × 10⁻⁴, consistent with that in methane obtained in previous studies. Possible sources of fractionation at different steps of the acetylene photochemistry are investigated.

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

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2407.20882 [astro-ph.EP] (or arXiv:2407.20882v1 [astro-ph.EP] for this version)
Related DOI:
https://doi.org/10.1016/j.icarus.2024.116221
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Submission history
From: Bruno Bézard
[v1] Tue, 30 Jul 2024 14:57:21 UTC (396 KB)
https://arxiv.org/abs/2407.20882
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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