The HCO radical was detected
in the ISM a long time ago. The detection of the
HCCO radical has been
reported fairly recently.
B. A. McGuire, A. M. Burkhardt, C. N. Shingledecker, S. V. Kalenskii, E. Herbst, A. J. Remijan, and M. C. McCarthy
reported on the
Detection of Interstellar HC5O in TMC-1 with the Green Bank Telescope
Astrophys. J. 843, Art. No. L28 (2017).
Two Λ-components, each consisting of two HFS components, of the J = 17/2 15/2 transition were detected in emission near 21.945 GHz.
In addition, the HC7O radical was tentatively detected through stacking the Λ-components of two transitions, J = 35/2 33/2 and 37/2 35/2 near 19.204 and 20.302 GHz, respectively. These reports may appear as space oddities, but we shall know more eventually.