Ethenone, H2CCO, aka ketene, had been identified first in spectra
recorded toward Sgr B2(OH) by
B. E. Turner,
Microwave Detection of Interstellar Ketene
Astrophys. J. 213, L75L79 (1977).
The NRAO 11 m telecope was employed to identify three Ka = 1 transitions with J' = 4 and 5. The fourth transition and the two Ka = 0 transitions were detected tentatively around 81 and 101 GHz.
Evidence for the J' = 4,
Ka = 0 and 1 transitions were
found in Orion A by:
L. E. B. Johansson, C. Andersson, J. Eldér, P. Friberg, Å. Hjalmarson, B. Höglund, W. M. Irvine, H. Olofsson, and G. Rydbeck,
Spectral Scan of Orion A and IRC +10216 from 72 to 91 GHz
Astron. Astrophys. 130, 227256 (1984).
It is also fairly abundant in dark clouds:
M. Ohishi, K. Kawaguchi, N. Kaifu, W. M. Irvine, Y. C. Minh, S. Yamamoto, S. Saito,
The Ortho to Para Ratio for Ketene in TMC-1
ASP Conf. Ser. 16, 387391 (1991).
It was also found in three translucent clouds (CB 17
CB 24, and CB 228):
B. E. Turner, R. Terzieva, and E. Herbst,
The Physics and Chemistry of Small Translucent Molecular Clouds. XII. More Complex Species Explainable by Gas-Phase Processes
Astrophys. J. 518, 699732 (1999).