J. Cernicharo, C. Cabezas, M. Agúndez, Y. Endo, B. Tercero, N. Marcelino and P. de Vicente
reported on the
QUIJOTE discovery of the cation radicals HC5N+ and HC7N+
Astron. Astrophys. 686, Art. No. L15 (2024).
HC₅N⁺ and HC₇N⁺ were identified through 7 and 8 unblended or slightly blended transitions in their ²Π_3/2 lower spin ladder, respectively, with 23/2 ≤ J ≤ 37/2 in the first case and 53/2 ≤ J ≤ 69/2 in the latter. The identifications were made 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. T_rot = 8.5 ± 0.5 K was derived for HC₅N⁺, while T_rot = 7.8 ± 0.1 K was derived for HC₇N⁺. The abundance ratios present a consistent and interesting picture. The HC₅N⁺ / HC₇N⁺ ratio is ~4.2; the HC₅N⁺ / HC₅N, HC₅N⁺ / C₅N⁻, and HC₅N⁺ / C₅N⁻ ratios are about 670, 4.8, and 1.2, respectively, while the HC₇N⁺ / HC₇N and HC₇N⁺ / C₇N⁻ ratios are about 1000 and 2.2, respectively.

Shortly thereafter,
C. Cabezas, M. Agúndez, Y. Endo, B. Tercero, N. Marcelino, P. de Vicente, and J. Cernicharo
published on the
Discovery of the interstellar cyanoacetylene radical cation HC3N+
Astron. Astrophys. 687, Art. No. L22 (2024).
The QUIJOTE survey of TMC-1 was employed once more to identify the six strong hyperfine structure components of the J = 7/2 − 5/2 near 31.63 GHz and 9/2 − 7/2 near 40.66 GHz in its ²Π_3/2 lower spin ladder with good signal-to-noise ratio. The HFS components where not or only slightly blended with the exception of one in the upper transition. Supporting, but less favorable results were presented for the 11/2 − 9/2 transition near 49.965 GHz. The rotational temperature was estimated to be 4.5 K. The HC₃N to HC₃N⁺ ratio is about 3200; the C₃N to HC₃N⁺ ratio about 300; the HC₃N⁺ to HC₅N⁺ ratio is about 0.6.

Contributor(s): H. S. P. Müller; 06, 2024; 07, 2024