Detection of Interstellar H2CCCHC3N

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Cyanoacetylene

The chemical pathways linking the small organic molecules commonly observed in molecular clouds to the large, complex, polycyclic species long-suspected to be carriers of the ubiquitous unidentified infrared emission bands remain unclear.

To investigate whether the formation of mono- and poly-cyclic molecules observed in cold cores could form via the bottom-up reaction of ubiquitous carbon-chain species with, e.g. atomic hydrogen, a search is made for possible intermediates in data taken as part of the GOTHAM (GBT Observations of TMC-1 Hunting for Aromatic Molecules) project. Markov-Chain Monte Carlo (MCMC) Source Models were run to obtain column densities and excitation temperatures. Astrochemical models were run to examine possible formation routes, including a novel grain-surface pathway involving the hydrogenation of C6N and HC6N, as well as purely gas-phase reactions between C3N and both propyne (CH3CCH) and allene (CH2CCH2), as well as via the reaction CN + H2CCCHCCH.

We report the first detection of cyanoacetyleneallene (H2CCCHC3N) in space toward the TMC-1 cold cloud using the Robert C. Byrd 100 m Green Bank Telescope (GBT). Cyanoacetyleneallene may represent an intermediate between less-saturated carbon-chains, such as the cyanopolyynes, that are characteristic of cold cores and the more recently-discovered cyclic species like cyanocyclopentadiene. Results from our models show that the gas-phase allene-based formation route in particular produces abundances of H2CCCHC3N that match the column density of 2×1011 cm−2 obtained from the MCMC Source Model, and that the grain-surface route yields large abundances on ices that could potentially be important as precursors for cyclic molecules.

C. N. Shingledecker, K. L. K. Lee, J. T. Wandishin, N. Balucani, A. M. Burkhardt, S. B. Charnley, R. Loomis, M. Schreffler, M. Siebert, M. C. McCarthy, B. A. McGuire

Comments: Accepted in A&A Letters
Subjects: Astrophysics of Galaxies (astro-ph.GA); Chemical Physics (physics.chem-ph)
Cite as: arXiv:2105.03347 [astro-ph.GA] (or arXiv:2105.03347v1 [astro-ph.GA] for this version)
Submission history
From: Christopher Shingledecker
[v1] Fri, 7 May 2021 16:00:19 UTC (7,767 KB)
https://arxiv.org/abs/2105.03347
Astrobiology, Astrochemistry,

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