Discovery Of Interstellar 2-Cyanoindene (2-C9H7CN) In GOTHAM Observations of TMC-1

By Keith Cowing
Press Release
September 15, 2022
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Discovery Of Interstellar 2-Cyanoindene (2-C9H7CN) In GOTHAM Observations of TMC-1
Corner plot for 2-C9H7CN showing parameter covariances and marginalized posterior distributions for the 2- C9H7CN MCMC fit. 16th, 50th, and 84th confidence intervals (corresponding to ±1 sigma for a Gaussian posterior distribution) are shown as vertical lines.

We present laboratory rotational spectroscopy of five isomers of cyanoindene (2-, 4-, 5-, 6-, and 7-cyanoindene) using a cavity Fourier-transform microwave spectrometer operating between 6-40 GHz.

Based on these measurements, we report the detection of 2-cyanoindene (1H-indene-2-carbonitrile; 2-C9H7CN) in GOTHAM line survey observations of the dark molecular cloud TMC-1 using the Green Bank Telescope at centimeter wavelengths. Using a combination of Markov Chain Monte Carlo (MCMC), spectral stacking, and matched filtering techniques, we find evidence for the presence of this molecule at the 6.3σ level.

This provides the first direct observation of the ratio of a cyano-substituted polycyclic aromatic hydrocarbon (PAH) to its pure hydrocarbon counterpart, in this case indene, in the same source. We discuss the possible formation chemistry of this species, including why we have only detected one of the isomers in TMC-1. We then examine the overall hydrocarbon:CN-substituted ratio across this and other simpler species, as well as compare to those ratios predicted by astrochemical models.

We conclude that while astrochemical models are not yet sufficiently accurate to reproduce absolute abundances of these species, they do a good job at predicting the ratios of hydrocarbon:CN-substituted species, further solidifying -CN tagged species as excellent proxies for their fully-symmetric counterparts.

Madelyn L. Sita, P. Bryan Changala, Ci Xue, Andrew M. Burkhardt, Christopher N. Shingledecker, Kin Long Kelvin Lee, Ryan A. Loomis, Emmanuel Momjian, Mark A. Siebert, Divita Gupta, Eric Herbst, Anthony J. Remijan, Michael C. McCarthy, Ilsa R. Cooke, Brett A. McGuire

Comments: Accepted in ApJL
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2209.06851 [astro-ph.GA] (or arXiv:2209.06851v1 [astro-ph.GA] for this version)
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Submission history
From: Brett McGuire
[v1] Wed, 14 Sep 2022 18:04:33 UTC (1,588 KB)
Astrobiology, Astrochemistry

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) 🖖🏻