Discovery Of The Interstellar Cyanoacetylene Radical Cation HC3N+

We report the first identification in space of HC₃N⁺, the simplest member of the family of cyanopolyyne cations. Three rotational transitions with half-integer quantum numbers from J=7/2 to 11/2 have been observed with the Yebes 40m radio telescope and assigned to HC₃N⁺, which has an inverted 2Π ground electronic state.

The three rotational transitions exhibit several hyperfine components due to the magnetic and nuclear quadrupole coupling effects of the H and N nuclei. We confidently assign the characteristic rotational spectrum pattern to HC₃N⁺ based on the good agreement between the astronomical and theoretical spectroscopic parameters.

We derived a column density of (6.0±0.6)×1010 cm−2 and a rotational temperature of 4.5±1\,K. The abundance ratio between HC₃N and HC₃N⁺ is 3200±320. As found for the larger members of the family of cyanopolyyne cations (HC₅N⁺ and HC₇N⁺), HC₃N⁺ is mainly formed through the reactions of H₂ and the cation C₃N⁺ and by the reactions of H+ with HC₃N. In the same manner than other cyanopolyyne cations, HC₃N⁺ is mostly destroyed through a reaction with H₂ and a dissociative recombination with electrons.

Observed transitions of HC₃N + in TMC-1 with F1 and F quantum numbers indicated. The abscissa corresponds to the rest frequency, and the ordinate is the antenna temperature corrected for atmospheric and telescope losses in milliKelvin. Blank channels correspond to negative features produced when folding the frequency-switched data. The red lines correspond to the synthetic spectra calculated for a column density of 6.0×1010 cm−2 and a rotational temperature of 4.5 K. — astro-ph.GA

C. Cabezas, M. Agúndez, Y. Endo, B. Tercero, N. Marcelino, P. de Vicente, J. Cernicharo

Comments: Accepted as a Letter to the Editor in Astronomy & Astrophysics on June 28th 2024
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2407.02121 [astro-ph.GA] (or arXiv:2407.02121v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2407.02121
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Submission history
From: Carlos Cabezas
[v1] Tue, 2 Jul 2024 10:11:46 UTC (54 KB)
https://arxiv.org/abs/2407.02121
Astrobiology, Astrochemistry,