Discovery of Interstellar 2-Cyanoindene (2-C${}_9$H${}_7$CN) in GOTHAM Observations of TMC-1

Abstract

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-C${}_9$H${}_7$CN) 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 6.3$\sigma$ 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.

Accepted in ApJL

References in corpus (9)

• Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
• Discovery of the Pure Polycyclic Aromatic Hydrocarbon Indene ($c$-C${}_9$H${}_8$) with GOTHAM Observations of TMC-1
• Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey
• A New Reference Chemical Composition for TMC-1
• Early Science from GOTHAM: Project Overview, Methods, and the Detection of Interstellar Propargyl Cyanide (HCCCH${}_2$CN) in TMC-1
• Aromatics and Cyclic Molecules in Molecular Clouds: A New Dimension of Interstellar Organic Chemistry
• What Produces Dust Polarization in the HH 212 Protostellar Disk at 878 μm: Dust Self-Scattering or Dichroic Extinction?
• Detection of Interstellar HC${}_4$NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions
• Discovery of CCS Velocity-Coherent Substructures in the Taurus Molecular Cloud 1

Cited by in corpus (9)

• Discovery of two cyano derivatives of acenaphthylene (C${}_{12}$H${}_8$) in TMC-1 with the QUIJOTE line survey
• Astronomical Detection of the Interstellar Anion C10H- towards TMC-1 from the GOTHAM Large Program on the GBT
• Aromatic cycles are widespread in cold clouds
• Detection of Interstellar $E$-1-cyano-1,3-butadiene in GOTHAM Observations of TMC-1
• Discovery of CH3CHCO in TMC-1 with the QUIJOTE line survey
• Low NH${}_3$/H${}_2$O ratio in comet C/2020 F3 (NEOWISE) at 0.7 au from the Sun
• CN and CCH derivatives of ethylene and ethane: Confirmation of the detection of CH${}_3$CH${}_2$CCH in TMC-1
• On the spectroscopy of phosphaalkynes: Millimeter- and submillimeter wave study of C2H5CP
• Concluding remarks: Faraday Discussion on astrochemistry at high resolution