Interstellar Detection of 2-Cyanocyclopentadiene, C${}_5$H${}_5$CN, a Second Five-Membered Ring Toward TMC-1

Abstract

Using radio observations with the Green Bank Telescope, evidence has now been found for a second five-membered ring in the dense cloud Taurus Molecular Cloud-1 (TMC-1). Based on additional observations of an ongoing, large-scale, high-sensitivity spectral line survey (GOTHAM) at centimeter wavelengths toward this source, we have used a combination of spectral stacking, Markov chain Monte Carlo (MCMC), and matched filtering techniques to detect 2-cyanocyclopentadiene, a low-lying isomer of 1-cyanocyclopentadiene, which was recently discovered there by the same methods. The new observational data also yields a considerably improved detection significance for the more stable isomer and evidence for several individual transitions between 23 - 32 GHz. Through our MCMC analysis, we derive total column densities of $8.3\times 10^{11}$ and $1.9\times 10^{11}$ cm${}^{-2}$ for 1- and 2-cyanocyclopentadiene respectively, corresponding to a ratio of 4.4(6) favoring the former. The derived abundance ratios point towards a common formation pathway - most likely being cyanation of cyclopentadiene by analogy to benzonitrile.

arXiv comment6 pages, 3 figures and 1 table in the main text. 2 tables and 2 figures in the Appendix. Accepted for publication in The Astrophysical Journal Letters. Supplementary data available in the DataVerse entry provided in text

References in corpus (7)

• emcee: The MCMC Hammer
• Detection of the Aromatic Molecule Benzonitrile ($c$-C${}_6$H${}_5$CN) in the Interstellar Medium
• Early Science from GOTHAM: Project Overview, Methods, and the Detection of Interstellar Propargyl Cyanide (HCCCH${}_2$CN) in TMC-1
• Benzonitrile as a proxy for benzene in the cold ISM: low temperature rate coefficients for CN + C${}_6$H${}_6$
• Precise dipole moment and quadrupole coupling constants of benzonitrile
• Spectral Tomography for the Line-of-Sight Structures of the Taurus Molecular Cloud 1
• Discovery of CCS Velocity-Coherent Substructures in the Taurus Molecular Cloud 1

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