===== On Cyclopentadiene in the ISM =====

J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, J. R. Pardo, and P. de Vicente\\
reported on\\
**[[https://doi.org/10.1051/0004-6361/202141156|Pure hydrocarbon cycles in TMC-1: Discovery of ethynylcyclopropenylidene, cyclopentadiene, and indene]]**\\
//Astron. Astrophys.// **649**, Art. No. L15 (2021).\\
Cyclopentadiene, //c//-C<sub>5</sub>H<sub>6</sub>, was identified through five unblended or slightly blended //b//-type lines with 2 ≤ //J// ≤ 5 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. One line corresponds to the unresolved //K<sub>c</sub>// = //J// = 5 − 4 asymmetry doublet. A value of //T//<sub>rot</sub> = 10 K was assumed. The column density of //c//-C<sub>5</sub>H<sub>6</sub> is about the same as the C<sub>4</sub>H<sub>4</sub> isomers butenyne and ethynylallene. It is about a factor of 7 lower than that of C<sub>3</sub>H<sub>3</sub> and about factors of 15 and 63 higher than the 1- and 2-cyano derivatives of //c//-C<sub>5</sub>H<sub>6</sub>.\\



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

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