===== On Ethynylallene in the ISM =====

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\\
**[[https://doi.org/10.1051/0004-6361/202140482|Discovery of allenyl acetylene, H<sub>2</sub>CCCHCCH in TMC-1 − study of the isomers of C<sub>5</sub>H<sub>4</sub>]]**\\
//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<sub>a</sub>// ≤ 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<sub>a</sub>// = 3 lines of these is on the edge, but the model supports the assignments. A value of //T//<sub>rot</sub> = 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).\\


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

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