Observed transitions of c-C₃H₂ in TMC-1. The abscissa corresponds to the rest frequency of the lines, assuming a local standard of rest velocity of the source of 5.77 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 (see text). Blue labels indicate the multiplicative factor applied, when needed, to the model to match the intensity of the observed lines.