Selected transitions of c-C₃HCCH in TMC-1. The abscissa corresponds to the rest frequency of the lines, assuming a local standard of rest velocity of the source of 5.83 km s⁻¹. Frequencies and intensities for the observed lines are given in Table A.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 left corner of the corresponding panel. The red lines show the computed synthetic spectrum for this species for T_r = 10 K and a column density of 3.1 × 10¹¹ cm⁻². Cyan labels indicate the multiplicative factor applied to the model to match the intensity of the observed lines.