J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, J. R. Pardo, and P. de Vicente
reported on
Pure hydrocarbon cycles in TMC-1: Discovery of ethynylcyclopropenylidene, cyclopentadiene, and indene
Astron. Astrophys. 649, Art. No. L15 (2021).
Indene, c-C9H8, was identified as the first pure polycyclic aromatic hydrocarbon through a large number of mostly a-type lines with 10 ≤ J ≤ 20 and Ka ≤ 6 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. A substantial fraction of the lines was unblended or slightly blended. A value of Trot = 10 K was assumed. The column density of indene is about the same as cyclopentadienene or the C4H4 isomers butenyne and ethynylallene. It is about a factor of 7 lower than that of C3H3.
A. M. Burkhardt, K. L. K. Lee, P. B. Changala, C. N. Shingledecker, I. R. Cooke, R. A. Loomis, H. Wei, S. B. Charnley, E. Herbst, M. C. McCarthy, and B. A. McGuire
submitted a report somewhat earlier but that appeared later on the
Discovery of the pure polycyclic aromatic hydrocarbon indene (//c//-C<sub>9</sub>H<sub>8</sub>) with GOTHAM observations of TMC-1
Astrophys. J. Lett. 913, Art. No. L18 (2021).
The observations were obtained in the course of the line survey Green Bank Telescope Observations of TMC-1: Hunting for Aromatic Molecules. The data were recorded with very high resolution which resolves, at least in part, the complex velocity structure . No individual lines were detected, as usually in this survey. Stacking of all lines of all four major velocity components, however, yielded a signal slighly above 5σ. Note, however, that this method becomes questionable with weak lines as those of indene. As can be seen in Fig. 4 of the previous paper, TMC-1 is not line poor anymore at 1 cm wavelength on the level of the indene lines; the situation may be slightly better at longer wavelengths. The derived column densities of the two reports agree.
Contributor(s): H. S. P. Müller; 05, 2021