On Cyclopropenylidene, c-C3H2, in Space

In 1985, several unidentified lines observed toward several sources, were assigned to the aromatic molecule cyclopropenylidene by
P. Thaddeus, J. M. Vrtilek, and C. A. Gottlieb,
Laboratory and Astronomical Identification of Cyclopropenylidene, C3H2,
Astrophys. J. 299, L63–L66 (1985).

The first observation of an initially unidentified line concerned one of the ortho ground state lines 212 – 101 in emission at 82093.54 GHz toward the diverse molecular clouds Ori A, Sgr B2(OH), and TMC-1 by
P. Thaddeus, M. Guélin, and R. A. Linke,
Three New 'Nonterrestrial' Molecules,
Astrophys. J. 246, L41–L45 (1981).

An interesting aspect has been found by
H. E. Matthews, S. C. Madden, L. W. Avery, and W. M. Irvine,
The C3H2 220 – 211 Transition: Absorption in Cold Dark Clouds,
Astrophys. J. 307, L69–L73 (1986).

Observations of the two 13C isotopomers of cyclopropenylidene were reported first by J. Gómez-González, M. Guélin, J. Cernicharo, C. Kahane, and M. Bogey,
Detection of Interstellar 13C Isotopes of C3H2,
Astron. Astrophys. 168, L11–L12 (1986).
They observed the 212 – 101 transitions toward Sgr B2(OH).

M. B. Bell, P. A. Feldman, H. E. Matthews, and L. W. Avery reported on the
Detection of Deuterated Cyclopropenylidene (C3HD) in TMC-1,
Astrophys. J. 311, L89–L92 (1986).
The detection of multiply substituted isotopologs is currently hampered by the lack of published laboratory data.

In 2012, laboratory data were published on several isotopologs, including the doubly deuterated one and the ones with one D and one 13C. However, data are still missing on the isotopomers with two 13C. It does not come as a surprise that
S. Spezzano, S. Brünken, P. Schilke, P. Caselli, K. M. Menten, M. C. McCarthy, L. Bizzocchi, S. P. Treviño-Morales, Y. Aikawa, and S. Schlemmer
reported on the
Interstellar Detection of c-C3D2,
Astrophys. J. 769, Art. No. L19 (2013)
in the dark clouds TMC-1C and L1544 using the IRAM 30 m radio telescope. Three transitions were detected in the 3 mm wavelength region.

Cyclopropenylidene was also detected in the circumstellar envelope of the carbon-rich AGB star CW Leo by
K. Kawaguchi, Y. Kasai, S.-I. Ishikawa, N. Kaifu,
A Spectral-Line Survey Observation of IRC +10216 between 28 and 50 GHz,
Publ. Astron. Soc. Japan 47, 853–876 (1995).

The molecule was also detected in the circumstellar envelope of a carbon-rich post-AGB star by
P. Cox, R. Güsten, and C. Henkel,
Detection of the Hydrocarbon Ring Molecule C3H2 in the Planetary Nebula NGC 7027,
Astron. Astrophys. 181, L19–L22 (1987).

P. Cox, R. Güsten, and C. Henkel reported on the
Observations of C3H2 in the Diffuse Interstellar Medium,
Astron. Astrophys. 206, 108–116 (1988).

Contributor(s): H. S. P. Müller; 03, 2011; 05, 2013