The 1,3-pentadiyne molecule CH₃C₄H, aka methyldiacetylene, had been identified in spectra recorded toward TMC-1 by two groups independently and at almost the same time
J. M. MacLeod, L. W. Avery, N. W. Broten,
The detection of interstellar methyldiacetylene (CH₃C₄H)
Astrophys. J. 282, L89–L92 (1984);
C. M. Walmsley, P. R. Jewell, L. E. Snyder, and G. Winnewisser,
Detection of interstellar methyldiacetylene (CH₃C₄H) in the dark dust cloud TMC 1
Astron. Astrophys. 184, L11–L14 (1984).

The molecule was also detected by
M. Araki, S. Takano, N. Sakai, S. Yamamoto, T. Oyama, N. Kuze, and K. Tsukiyama,
who studied
Long Carbon Chains in the Warm Carbon-chain-chemistry Source L1527: First Detection of C₇H in Molecular Clouds,
Astrophys. J. 847 Art. No. 51 (2017).
The three J = 11 – 10 transitions with K = 0, 1, and 2 were detected near 44.8 GHz with the 100 m GBT.

C. Cabezas, R. Fuentetaja, E. Roueff, M. Agúndez, B. Tercero, N. Marcelino, J. R. Pardo, P. de Vicente and J. Cernicharo
reported on
New Deuterated Species in TMC-1: Detection of CH₂DC₄H with the QUIJOTE line survey,
Astron. Astrophys. 657 Art. No. L5 (2022).
Twelve transition with J = 8 to 12 and K_a ≤ 1 were detected with the Yebes 40 m radio telescope. The CH₃C₄H to CH₂DC₄H abundance ratio of 24 ± 2 is very similar to that of CH₃C₃N to CH₂DC₃N ratio of 22 ± 2.

Contributor(s): H. S. P. Müller; 7, 2004; 10, 2017; 03, 2022