M. Agúndez, C. Cabezas, N. Marcelino, R. Fuentetaja, B. Tercero, P. de Vicente, and J. Cernicharo
reported on
Discovery of Interstellar NC₄NH⁺: Dicyanopolyynes are indeed Abundant in Space,
Astron. Astrophys. 669, Art. No. L1 (2023).
Six consecutive transitions with 12 ≤ J“ ≤ 17 between 33.6 and 46.6 GHz were identified in the course of a molecular line survey of the prototypical cold dark molecular cloud TMC-1 carried out with the Yebes 40 m radio telescope between 31.0 and 50.3 GHz with good signal-to-noise ratio, except for the highest J, where it was still reasonable. The molecule was identified based on the proximity of the astronomically derived spectroscopic parameters to scaled ones from a quantum-chemical calculation. The parameters of HC₅NH⁺, for which also no laboratory data are available at present, are very similar. However, the scaled parameters agree much better with those from astronomical observations with the current identifications. Additional support come from the fact that the molecule with the larger dipole moment, NC₄NH⁺, has a rotation temperature of ∼6 K whereas the one of HC₅NH⁺ is ~8 K. NC₄NH⁺ is about eight times less abundant in TMC-1 than NC₂NH⁺.

Contributor(s): H. S. P. Müller; 12, 2022