On the Detection of Heptatriynylidyne, C₇H, in Space

The heptatriynylidyne radical in its ²Π_r 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 L1–L4 (1997).

It appears as if this is the only C_nH radical that has been detected toward IRC +10216 and not toward TMC-1.