L. W. Avery, N. W. Broten, J. M. McLeod, T. Oka, and H. W. Kroto
reported on the
Detection of the Heavy Interstellar Molecule Cyanodiacetylene
Astrophys. J. 205, L173–L175 (1976).
The J = 4 – 3 transition near 10.651 GHz was observed in emission toward Sagittarius (Sgr) B2 employing the 46 m radio telecope of the Algonquin Radio Observatory.

N. W. Broten, J. M. McLeod, T. Oka, L. W. Avery, J. W. Brooks, R. X. McGee, and L. M. Newton
reported subsequently on
Evidence for Weak Maser Action in Interstellar Cyanodiacetylene
Astrophys. J. 209, L143–L147 (1976).
The J = 8 – 7 transition near 21.301 GHz was observed toward Sagittarius /Sgr) B2 employing the 46 m radio telecope of the Algonquin Radio Observatory. In addition, the Parkes 64 m dish was used to study the The J = 1 – 0 transition near 2.663 GHz with well-resolved hyperfine structure. The high intensity of the latter emission lines were viewed as evidence for weak maser activity.

L. T. Little, P. W. Riley, and D. N. Matheson
reported on the
Detection of the //J// = 9 → 8 Transition of Interstellar Cyanodiacetylene
Mon. Not. R. Astron. Soc. 181, 33P–35P (1977).
TMC-1 was observed with the 25 m dish of the Chilbolton Observatory. The authors mention an earlier report by J. M. MacLeod et al. at an IAU meeting.

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 HC₅N and HC₇N in IRC +10216
Astron. Astrophys. 70, L37–L39 (1978).
The J = 9 – 8 transition near 23.964 GHz was detected for the smaller polyyne.
As HC₃N and HC₇N earlier, HC₅N has also been detected in protoplanetary nebulae such as CRL 2688, CRL 618 in 1988 and others later.

The detection of DC₅N in TMC-1 was reported by two groups simultaneously:
J. M. MacLeod, L. W. Avery, and N. W. Broten,
//Astrophys. J.// 251, L33–L36 (1981); and
F. P. Schloerb, R. L. Snell, W. D. Langer, and J. S. Young,
//Astrophys. J.// 251, L37–L41 (1981).
The inferred D/H ratio is slightly higher than 0.01.

S. Takano, H. Suzuki, M. Ohishi, S.-I. Ishikawa, N. Kaifu, Y. Hirahara, and A. Masuda
used the Nobeyama 45 m telescope for the
Detection of Five ¹³C Isotopic Species of HC₅N in TMC-1
Astrophys. J. 361, L15–L18 (1990).
The J = 14 – 13 transitions bewteen 36 and 38 GHz were detected at intensities compatible with the ¹²C/¹³C ratio in the solar neighborhood.

K. Taniguchi and M. Saito
reported on the
First Detection of HC₅¹⁵N in the Interstellar Medium
Publ. Astron. Soc. Japan 69, Art. No. L7 (2017).
The Nobeyama 45 m telescope was used to detect the J = 9 – 8 transition near 23.375 GHz. The ¹⁴N/¹⁵N ratio derived via the ¹³C isotopomers is 344±53, slightly lower than 440 in the local ISM. In the case of HC₃N, they determined a ratio of 257±54.

Vibrationally excited molecules have been detected with the IRAM 30 m telescope in the circumstellar envelope of the carbon-rich post-AGB star V353 Aur, which is somewhat better known as CRL 618, by
J. R. Pardo, J. Cernicharo, and J. R. Goicoechea,
Observational Evidence of the Formation of Cyanopolyynes in CRL 618 through the Polymerization of HCN
Astrophys. J. 628, 275–282 (2005).
Four low-lying states (v₁₁ = 1 to 3 and v₁₀ = 1) were detected with vibrational energies of up to about 315 cm^–1.

Contributor(s): H. S. P. Müller; 01, 2018.