Laboratory and astronomical detection of the cyclic C3H radical

The rotational spectrum of the cyclic C₃H radical was detected in the laboratory and in interstellar space. The radical was produced in the laboratory by discharging a mixture of C₂H₂, CO, and He. Forty-nine lines were assigned, and the molecular constants were precisely determined. The astronomical search was made using the 2₁₂-1₁₁ transition at 91.5 GHz, and its four fine and hyperfine components were detected toward TMC-1. The column density of cyclic C₃H is estimated to be 6×10¹²cm⁻², which is comparable to that of the linear C₃H.