Detectable Abundance of Cyanoacetylene (HC$_3$N) Predicted on Reduced Nitrogen-Rich Super-Earth Atmospheres

Abstract

We predict that cyanoacetylene (HC 3 N) is produced photochemically in the atmosphere of GJ 1132 b in abundances detectable by the James Webb Space Telescope (JWST), assuming that the atmosphere is as described by Swain et al. (2021). First, we construct line list and cross-sections for HC 3 N. Then we apply these cross-sections and the model atmosphere of Swain et al. (2021) to a radiative transfer model in order to simulate the transmission spectrum of GJ 1132 b as it would be seen by JWST, accounting for the uncertainty in the retrieved abundances. We predict that cyanoacetylene features at various wavelengths, with a clear lone feature at 4.5 µm, observable by JWST after four transits. This feature persists within the 1 − σ uncertainty of the retrieved abundances of HCN and CH 4 .

Synchrotron-based far-infrared spectroscopy of HC3N: Extended ro-vibrational analysis and new line list up to 3360 cm−1<

“…of the chemical evolution of molecular clouds [5] or -through the DC 3 N isotopologue -as proxy of the deuteration level prior to the formation of dense gas in star-forming regions [6]. Moreover, cyanoacetylene emission has been used to unravel the seasonal changes and atmospheric dynamics of the largest Saturn's moon Titan [7] and is predicted to be detectable in Super-Earth atmospheres by upcoming James Webb Telescope observations [8]. Interestingly, vibrationally excited HC 3 N has been also observed in Space.…”