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.