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, 11321139 (2008).
This anion is isolelectronic to C4H. Besides the presently more common C2nH family, it is the first member of a second family of anions detected in space, C2n1N.
It was searched for, but not found in TMC-1.