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 (13)

• 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
• The interstellar chemistry of C3H and C3H2 isomers
• 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 (22)

• 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
• The sulphur saga in TMC-1: Discovery of HCSCN and HCSCCH
• 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
• Machine Learning of Interstellar Chemical Inventories
• Detection of Interstellar $E$-1-cyano-1,3-butadiene in GOTHAM Observations of TMC-1
• Multiply charged naphthalene and its C10H8 isomers: bonding, spectroscopy and implications in AGN environments
• Energetic Electron Irradiations of Amorphous and Crystalline Sulphur-Bearing Astrochemical Ices
• 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?
• Astrochemical model to study the abundances of branched carbon-chain molecules in a hot molecular core with realistic binding energies
• 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
• Chemical variations across the TMC-1 boundary: molecular tracers from translucent phase to dense phase
• Laser-induced fragmentation of coronene cations
• 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
• Concluding remarks: Faraday Discussion on astrochemistry at high resolution