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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 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.

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