J. Cernicharo, R. Fuentetaja, C. Cabezas, M. Agúndez, N. Marcelino, B. Tercero, J. R. Pardo, and P. de Vicente
reported on
Discovery of allenyl acetylene, H₂CCCHCCH in TMC-1 − study of the isomers of C₅H₄
Astron. Astrophys. 647, Art. No. L3 (2021).
Ethynylallene, aka allenylacetylene or 1,2-pentadien-4-yne, was identified through 16 unblended or slightly blended a-type transitions with 6 ≤ J ≤ 10 and K_a ≤ 3 in the course of a molecular line survey of the prototypical cold dark molecular cloud TMC-1 carried out with the Yebes 40 m radio telescope between 32.8 and 49.2 GHz. The signal-to-noise ratio of the K_a = 3 lines of these is on the edge, but the model supports the assignments. A value of T_rot = 9 ± 1 K was derived through a rotation diagram, but the model is more compatible with 7 K. The column density of butenyne is about a factor of 4.5 higher than that of the isoelectronic allenyl cyanide. It is, in addition, similar to that of butenyne, a factor of 5 lower than that of the methyldiacetylene isomer (aka butadienyne), and a factor of 10 lower than that of methylacetylene (aka propyne).

Contributor(s): H. S. P. Müller; 07, 2022