J. Cernicharo, C. Cabezas, M. Agúndez, B. Tercero, N. Marcelino, J. R. Pardo, F. Tercero, J. D. Gallego, J. A. López-Pérez, 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).

R. Fuentetaja, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, J. R. Pardo, P. de Vicente and J. Cernicharo
announced the
Discovery of allenyl acetylene, Discovery of HCCCH₂CCH in TMC-1 with the QUIJOTE line survey
Astron. Astrophys. 688, Art. No. L15 (2024).
1,4-Pentadiyne was identified through 18 mostly unblended or slightly blended b-type transitions with 2 ≤ J ≤ 12 and K_a ≤ 2 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 31.5 and 49.6 GHz. A value of T_rot = 9.5 ± 0.5 K was derived. The column density of 1,4-pentadiyne is about a factor of 1.4 higher than that of the isoelectronic mono cyanide and about a factor of 1.4 less abundant than the ethynylallene isomer.

Contributor(s): H. S. P. Müller; 05, 2021; 08, 2024