===== On the Detection of Cyanooctatetrayne, HC9N, in Space =====

N. W. Broten, T. Oka, L. W. Avery, J. M. MacLeod, and H. W. Kroto,\\
**[[https://ui.adsabs.harvard.edu/abs/1978ApJ...223L.105B|The Detection of HC<sub>9</sub>N in Interstellar Space]]**\\
//Astrophys. J.// **223**, L105–L107 (1978)\\
reported the first detection of this cyanopolyyne in two transitions (//J// = 18 – 17 and 25 – 24 near 10.5 and 14.5 GHz, respectively) in Heile's Cloud 2 employing the 46 m radio telecope of the Algonquin Radio Observatory before the molecules was detected in the laboratory. The spectroscopic parameters were estimated from the smaller cyanopolyynes. Heile's Cloud 2 is better known as TMC-1.

More recently, the molecule was also detected in six transitions in the circumstellar shell of the famous carbon star CW Leo:\\
M. B. Bell, L. W. Avery, J. M. MacLeod, and H. E. Matthews,\\
**[[https://ui.adsabs.harvard.edu/abs/1992ApJ...400..551B|The Excitation Temperature of HC<sub>9</sub>N in the Circumstellar Envelope of IRC +10216]]**\\
//Astrophys. J.// **400**, 551–555 (1992).\\

Truong-Bach, D. Graham, and Nguyen-Q-Rieu,\\
**[[https://ui.adsabs.harvard.edu/abs/1993A%26A...277..133T|HC<sub>9</sub>N from the Envelopes of IRC +10216 and CRL 2688]]**\\
//Astron. Astrophys.// **277**, 133–138 (1993);\\
detected one additional higher-//J// transition toward the former source and the same transition in a protoplanetary nebula.\\

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\\
**[[https://doi.org/10.1051/0004-6361/202038571|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 HC<sub>9</sub>N in its lowest excited state //v//<sub>19</sub> = 1 were detected despite the low rotational temperature. The lines could be assigned unambiguously although no laboratory data were available for this excited state. The derived HC<sub>5</sub>N to HC<sub>7</sub>N ratio is extremely low, roughly 2.4. The derived HC<sub>7</sub>N to HC<sub>9</sub>N ratio is still very low, roughly 7.7.\\


----

Contributor(s): H. S. P. Müller; 02, 2006; 06, 2009; 08, 2020.

----