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,
Astronomical Detection of the HCCN Radical Toward a New Family of Carbon-Chain Molecules ?
Astron. Astrophys. 244, L21L24 (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 HC4N, see below.
Two features near 110 GHz detected toward Sgr B2 and Orion A are due to a minor velocity component of C18O and vibrationally excited HC3N, 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,
Detection of the Linear Radical HC4N in IRC +10216
Astrophys. J. 615, L145L148 (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 HC3N in this source.