The cyanoethynylide ion has been detected toward the carbon rich star IRC +10216 in 4 rotational transitions from J = 10 – 9 to 15 – 14 which occur in the 3 and 2 mm regions:
P. Thaddeus, C. A. Gottlieb, H. Gupta, S. Brünken, M. C. McCarthy, M. Agúndez, M. Guélin, and J. Cernicharo,
Laboratory and Astronomical Detection of the Negative Molecular Ion C₃N^–
Astrophys. J. 677, 1132–1139 (2008).
This anion is isolelectronic to C₄H^–. Besides the presently more common C_2nH^– family, it is the first member of a second family of anions detected in space, C_2n–1N^–.
It was searched for, but not found in TMC-1.

Contributor(s): H. S. P. Müller; 4, 2008