The heptatriynylidyne radical in its 2Πr state
has been detected in five lines of three rotational transitions toward
IRC +10216 by
M. Guélin, J. Cernicharo, M. J. Travers, M. C. McCarthy, C. A. Gottlieb, P. Thaddeus, M. Ohishi, S. Saito, and S. Yamamoto,
Detection of a new Linear Carbon Chain Radical: C7H,
Astron. Astrophys. 317 L1L4 (1997).
It appears as if this is the only CnH radical that has been detected toward IRC +10216 and not toward TMC-1.