On the Detection of Cyanohexatriyne, HC7N, in the ISM

H. W. Kroto, C. Kirby, D. R. M. Walton, L. W. Avery, N. W. Broten, J. M. MacLeod, and T. Oka,
The Detection of Cyanohexatriyne, H(C≡C)<sub>3</sub>CN, in Heile's Cloud 2
Astrophys. J. 219, L133–L137 (1978)
reported the first detection of this cyanopolyyne in two transitions (J = 9 – 8 and 21 – 20 near 10.15 and 23.69 GHz, respectively) in Heile's Cloud 2 employing the 46 m radio telecope of the Algonquin Radio Observatory.

More recently, the Effelsberg 100 m telecope was used to study the circumstellar shell of the famous carbon star CW Leo:
G. Winnewisser and C. M. Walmsley,
The Detection of HC<sub>5</sub>N and HC<sub>7</sub>N in IRC +10216
Astron. Astrophys. 70, L37–L39 (1978).
The J = 21 – 10 transition near 23.688 GHz was detected for the larger polyyne.

The molecule has also been detected with the Effelsberg 100 m telescope in the circumstellar envelope of the carbon-rich post-AGB star V1610 Cyg, which is somewhat better known as CRL 2688, by
Nguyen-Q-Rieu, D. Graham, and V. Bujarrabal,
Ammonia and Cyanotriacetylene in the Envelopes of CRL 2688 and IRC +10216
Astron. Astrophys. 138, L5–L8 (1984).

G. Langston and B. E. Turner described the
Detection of <sup>13</sup>C Isotopomers of the Molecule HC<sub>7</sub>N
Astrophys. J. 658, 455–461 (2007).
They searched for the J = 12 – 11 and 13 – 12 transitions in TMC-1 using the GBT 100 m telescope. No individual isotopomer was found. Instead, a barely significant signal was obtained by averaging all observations.

DC7N and (individually) 6 of the 7 13C isotopomers were detected in the study
Detection of HC<sub>5</sub>N and HC<sub>7</sub>N Isotopologues in TMC-1 with the Green Bank Telescope
Mon. Not. R. Astron. Soc. 474, 5068–5075 (2018); by
A. M. Burkhardt, E. Herbst, S. V. Kalenskii, M. C. McCarthy, A. J. Remijan, and B. A. McGuire.

J. R. Pardo, C. Bermúdez, C. Cabezas, M. Agúndez, J. D. Gallego, J. P. Fonfría, L. Velilla-Prieto, G. Quintana-Lacaci, B. Tercero, M. Guélin, and J. Cernicharo
reported on the
Detection of Vibrationally Excited HC<sub>7</sub>N and HC<sub>9</sub>N in IRC +10216
Astron. Astrophys. 640, Art. No. L13 (2020).
The authors carried out an unbiased molecular line survey with the Yebes 40 m dish between 31 and 50 GHz toward the circumstellar envelope of the famous C-rich AGB star CW Leonis. Numerous transitions of HC7N in its lowest excited state v15 = 1 were detected despite a rotational temperature of around 25 K. The derived HC5N to HC7N ratio is extremely low, roughly 2.4. The derived HC7N to HC9N ratio is still very low, roughly 7.7.


Contributor(s): H. S. P. Müller; 04, 2012; 01, 2018; 08, 2020.