Fine and hyperfine components of the 2_1, 1 − 1_1, 1 transition of c-C₃H in TMC-1 as observed with the Yebes 40 m radio telescope. The abscissa corresponds to the rest frequency of the lines, assuming a local standard of rest velocity of the source of 5.83 km s⁻¹. The ordinate is the antenna temperature, corrected for atmospheric and telescope losses, in millikelvins. The quantum numbers for each transition are indicated in the upper or lower right corner of the corresponding panel. The red line shows the computed synthetic spectrum for this species for a column density of 6.2 × 10¹² cm⁻² and T_r = 3.7 K (see text).