Propadienylidene is a higher energy isomer of the earlier detected, rather ubiquitous cyclopropenylidene.
J. Cernicharo, C. A. Gottlieb, M Guélin, T. C. Killian, G. Paubert, P. Thaddeus, and J. M. Vrtilek,
reported on the
Astronomical Detection of H₂CCC,
Astrophys. J. 368, L39–L41 (1991)
The para ground state transition 1_0,1 – 0_0,0 near 20.8 GHz was detected with the Effelsberg 100 m telescope in emission together with the ortho transitions 5_1,5 – 4_1,4, 5_1,4 – 4_1,3, and 7_1,6 – 6_1,5 near 103.0, 104.9, and 146.9 GHz, respectively. These transitions were made with the IRAM 30 m telescope. The molecule may have been detected also in the circumstellar envelope of CW Leonis, also known as IRC +10216.

J. Cernicharo, P. Cox, D. Fossé and R. Güsten,
reported on the
Detection of Linear C₃H₂ in Absorption toward Continuum Sources,
Astron. Astrophys. 351, 341–346 (1999)
The 1_0,1 – 0_0,0 transition was observed in absorption toward the continuum sources W49, W51e1/e2 and W51D.

The Molecule was also deteceted in a source of Warm Carbon Chain Chemistry by
N. Sakai, T. Sakai, T. Hirota, and S. Yamamoto,
Abundant Carbon-Chain Molecules toward the Low-Mass Protostar IRAS 04368+2557 in L1527,
Astrophys. J. 672, 371–381 (2008)

The Molecule was also deteceted in the CO⁺ peak of the Orion Bar photodissociation regions by
S. Cuadrado, J. R. Goicoechea, P. Piller, J. Cernicharo, A. Fuente, and C. Joblin,
The Chemistry and Spatial Distribution of Small Hydrocarbons in UV-irradiated Molecular Clouds: the Orion Bar PDR,
Astron. Astrophys. 575, Art. No. A82 (2015)

S. Spezzano, H. Gupta, S. Brünken, C. A. Gottlieb, P. Caselli, K. M. Menten, H. S. P. Müller, L. Bizzocchi, P. Schilke, M. C. McCarthy, and S. Schlemmer,
reported on the
A Study of the C₃H₂ Isomers and Isotopologues: First Interstellar Detection of HDCCC,
Astron. Astrophys. 575, Art. No. A110 (2016)
The 5_0,5 – 4_0,4 transition near 96.9 GHz was detected with the IRAM 30 m telescope in emission toward the starless cores TMC-1C and L1544. In addition, the 1_0,1 – 0_0,0 transition near 19.4 GHz was detected in TMC-1 with the 100 m GBT.

Contributor(s): H. S. P. Müller; 02, 2016