===== On the Detection of the HC2nN Radicals in Space =====

The cyanomethylene radical HCCN was observed with the IRAM 30 m telescope in the outer part of the circumstellar shell of the carbon-rich late-type star CW Leo, also known as IRC +10216, by\\
M. Guélin and J. Cernicharo,\\
**[[https://ui.adsabs.harvard.edu/abs/1991A%26A...244L..21G|Astronomical Detection of the HCCN Radical – Toward a New Family of Carbon-Chain Molecules ?]]**\\
//Astron. Astrophys.// **244**, L21–L24 (1991).\\
9 fine structure components of 4 rotational transitions (//N// = 4 – 3 to 7 – 6) between 87 and 154 GHz were not or not significantly blended. A rotational temperature of 12±4 K was derived which was modified slightly to 15±2 K in the letter describing the detection of HC<sub>4</sub>N, see below.\\
Two features near 110 GHz detected toward Sgr B2 and Orion A are due to a minor velocity component of C<sup>18</sup>O and vibrationally excited HC<sub>3</sub>N, respectively.

More recently, the detection of the next member, cyanoethynylmethylene, was also detected with the same instrument in the outer part of the circumstellar shell of CW Leo:\\
J. Cernicharo, M. Guélin, and J. R. Pardo,\\
**[[https://doi.org/10.1086/426439|Detection of the Linear Radical HC<sub>4</sub>N in IRC +10216]]**\\
//Astrophys. J.// **615**, L145–L148 (2004).\\
12 fine structure components of 4 rotational transitions (//N// = 18 – 17 to 21 – 20) between 82 and 97 GHz were detected; 4 lines were partially blended. A rotational temperature of 25±4 K was derived, similar to that of HC<sub>3</sub>N in this source.


----

Contributor(s): H. S. P. Müller; 11, 2004; 01, 2012

----