===== Reports on the Detection of 1,3-Pentadiyne in the ISM ===== 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,\\ **[[https://ui.adsabs.harvard.edu/abs/1984ApJ...282L..89M|The detection of interstellar methyldiacetylene (CH₃C₄H)]]**\\ //Astrophys. J.// **282**, L89–L92 (1984);\\ C. M. Walmsley, P. R. Jewell, L. E. Snyder, and G. Winnewisser,\\ **[[https://ui.adsabs.harvard.edu/abs/1984A%26A...134L..11W|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\\ **[[https://doi.org/10.3847/1538-4357/aa8637|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\\ **[[https://doi.org/10.1051/0004-6361/202142814|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.\\ \\ More recently,\\ C. Cabezas, M. Agúndez, E. Roueff, R. Fuentetaja, B. Tercero, N. Marcelino, P. de Vicente, and J. Cernicharo\\ announced the\\ **[[https://doi.org/10.1051/202557754|Detection of Six Isotopologues of CH₃CCCCH in TMC-1 with the QUIJOTE Line Survey]]**,\\ //Astron. Astrophys.// **703** Art. No. L22 (2025).\\ With an increase of the signal-to-noise ratio in comparison to the previous item, the authors were able to identify transition with //J// = 8 to 12 and //K_a// ≤ 1 of all five singly substituted ¹³C isotopologs and of CH₃C₄D with reasonable to good S/N and mostly not or only slightly blended. The lowest //J// pair of CH₃C₄D transitions was not covered. The ¹²C/¹³C ratio is 93 ± 11, while the H/D ratio in the case of CH₃C₄D is 54 ± 8.\\ \\ ---- Contributor(s): H. S. P. Müller; 7, 2004; 10, 2017; 03, 2022; 11, 2025 ----