Dicarbon monoxide (C₂O) was detected in the cold, dark cloud TMC-1 by Ohishi et al. in 1991. The detection was based on two rotational lines that were assigned with the spectrum measured by Yamada et al. and published in 1985. The first line was observed in 1988 with the 45 m telescope at Nobeyama Observatory and confirmed a few months later in 1989. The second transition was observed with the 43 m telescope at Green Bank Observatory in 1991. No further observations have been reported to date.