Discovery of the Pure Polycyclic Aromatic Hydrocarbon Indene ($c$-C${}_9$H${}_8$) with GOTHAM Observations of TMC-1

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs) have long been invoked in the study of interstellar and protostellar sources, but the unambiguous identification of any individual PAH has proven elusive until very recently. As a result, the formation mechanisms for this important class of molecules remain poorly constrained. Here we report the first interstellar detection of a pure hydrocarbon PAH, indene (C${}_9$H${}_8$), as part of the GBT Observations of TMC-1: Hunting for Aromatic Molecules (GOTHAM) survey. This detection provides a new avenue for chemical inquiry, complementing the existing detections of CN-functionalized aromatic molecules. From fitting the GOTHAM observations, indene is found to be the most abundant organic ring detected in TMC-1 to date. And from astrochemical modeling with NAUTILUS, the observed abundance is greater than the model's prediction by several orders of magnitude suggesting that current formation pathways in astrochemical models are incomplete. The detection of indene in relatively high abundance implies related species such as cyanoindene, cyclopentadiene, toluene, and styrene may be detectable in dark clouds.

18 pages, 2 figures and 3 tables in the main text. 1 table and 1 figure in the Appendix. Published in The Astrophysical Journal Letters. Supplementary data available in the DataVerse entry provided in text

References in corpus (15)

• Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
• Formation and destruction of polycyclic aromatic hydrocarbon clusters in the interstellar medium
• Early Science from GOTHAM: Project Overview, Methods, and the Detection of Interstellar Propargyl Cyanide (HCCCH${}_2$CN) in TMC-1
• Efficient Production of S${}_8$ in Interstellar Ices: The effects of cosmic ray-driven radiation chemistry and non-diffusive bulk reactions
• Benzonitrile as a proxy for benzene in the cold ISM: low temperature rate coefficients for CN + C${}_6$H${}_6$
• The interstellar chemistry of C3H and C3H2 isomers
• The Horizon Run 5 Cosmological Hydrodynamic Simulation: Probing Galaxy Formation from Kilo- to Giga-parsec Scales
• Discovery of CH2CHCCH and detection of HCCN, HC4N, CH3CH2CN, and, tentatively, CH3CH2CCH in TMC-1
• 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
• A study of C4H3N isomers in TMC-1: line by line detection of HCCCH2CN
• Detection of Interstellar HC${}_5$O in TMC-1 with the Green Bank Telescope
• Detection of HC${}_5$N and HC${}_7$N Isotopologues in TMC-1 with the Green Bank Telescope
• Study of the chemical evolution and spectral signatures of some interstellar precursor molecules of adenine, glycine alanine
• Discovery of CCS Velocity-Coherent Substructures in the Taurus Molecular Cloud 1

Cited by in corpus (49)

• 2021 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules
• Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey
• Discovery of Interstellar 2-Cyanoindene (2-C${}_9$H${}_7$CN) in GOTHAM Observations of TMC-1
• Discovery of the 7-ring PAH Cyanocoronene (C${}_{24}$H${}_{11}$CN) in GOTHAM Observations of TMC-1
• PHANGS-JWST First Results: Destruction of the PAH molecules in HII regions probed by JWST and MUSE
• The sulphur saga in TMC-1: Discovery of HCSCN and HCSCCH
• A Search for Heterocycles in GOTHAM Observations of TMC-1
• Carbon-Chain Chemistry in the Interstellar Medium
• The Mystery of Unidentified Infrared Emission Bands
• Aromatic cycles are widespread in cold clouds
• Detection of the propargyl radical at lambda 3 mm
• Discovery of a new molecular ion, HC7NH+, in TMC-1
• Discovery of interstellar phenalene ($c$-C${}_{13}$H${}_{10}$): A new piece for the chemical puzzle of PAHs in space
• Machine Learning of Interstellar Chemical Inventories
• Detection of Interstellar $E$-1-cyano-1,3-butadiene in GOTHAM Observations of TMC-1
• Toward the limits of complexity of interstellar chemistry: Rotational spectroscopy and astronomical search for n- and i-butanal
• CH3-Terminated Carbon Chains in the GOTHAM Survey of TMC-1: Evidence of Interstellar CH3C7N
• Energetic Electron Irradiations of Amorphous and Crystalline Sulphur-Bearing Astrochemical Ices
• Multiply charged naphthalene and its C10H8 isomers: bonding, spectroscopy and implications in AGN environments
• Oxygen-bearing organic molecules in comet 67P's dusty coma: first evidence for abundant heterocycles
• Comparative Electron Irradiations of Amorphous and Crystalline Astrophysical Ice Analogues
• Detection of Cosmic Fullerenes in the Almahata Sitta Meteorite: Are They an Interstellar Heritage?
• Gas-phase spectroscopy of photostable PAH ions from the mid- to far-infrared
• Sensitivity Analysis of Aromatic Chemistry to Gas-Phase Kinetics in a Dark Molecular Cloud Model
• Astrochemical model to study the abundances of branched carbon-chain molecules in a hot molecular core with realistic binding energies
• Astrochemical Modeling of Propargyl Radical Chemistry in TMC-1
• Formation of c-C6H5CN ice using the SPACE TIGER experimental setup
• Machine-learning identified molecular fragments responsible for infrared emission features of polycyclic aromatic hydrocarbons
• Infrared spectra of solid indene pure and in water ice. Implications for observed IR absorptions in TMC-1
• Laboratory rotational spectroscopy and astronomical search of ethynyl substituted naphthalene
• A search for the three isomers of cyano-1,3-butadiene in TMC-1: Implications for bottom-up routes involving 1,3-butadiene
• Polycyclic aromatic hydrocarbons destruction in star-forming regions across 42 nearby galaxies
• Laser-induced fragmentation of coronene cations
• Chemical variations across the TMC-1 boundary: molecular tracers from translucent phase to dense phase
• Diffuse interstellar bands as dust indicators: the contribution from 3D maps
• Infrared Spectroscopy of Pentagon-Containing PAHs: Indenyl and Fluorenyl Anions and Indenyl Cation
• CN and CCH derivatives of ethylene and ethane: Confirmation of the detection of CH${}_3$CH${}_2$CCH in TMC-1
• Photocleavage of aliphatic C--C bonds in the interstellar medium
• The End of the Road for Far-infrared Reddening Maps? Evidence for Reddening Errors Driven by Changes in PAH Abundance
• Polyaromatic Hydrocarbons with an Imperfect Aromatic System as Catalysts of Interstellar H${}_2$ Formation
• Long-Lived Isomers of C${}_{11}$H${}_9^{+}$: New Experimental Insights from the PIRENEA Setup
• Aromatic Species in the Molecular Universe
• In situ characterization of volatile and refractory hydrocarbons produced by UV photolysis of interstellar C${}_2$H${}_2$ ice
• Superhydrogenation of indene at low temperatures
• Searching for Corannulene with ALMA: Observations of the Red Rectangle Nebula
• Concluding remarks: Faraday Discussion on astrochemistry at high resolution
• Formation of methane and cyclohexane through the hydrogenation of toluene
• Acenaphthene Derivatives as Signatures of C${}_{11}$H${}_9^{+}$ Reactivity with Methylated Naphthalenes
• Rotational Spectra and Search for Aromatic Imines: 9-Iminofluorene and Benzophenone imine