Selected transitions of HCCCCS in TMC-1. The abscissa corresponds to the rest frequency of the lines. Frequencies and intensities for all observed lines are given in Table A.1. The ordinate is the antenna temperature, corrected for atmospheric and telescope losses, in millikelvin. The quantum numbers of each transition are indicated in the corresponding panel. The red line shows the computed synthetic spectra for this species for T_rot = 10 K and a column density of (9.5±0.8) × 10¹⁰ cm⁻². Blanked channels correspond to negative features produced when folding the frequency-switched data. Green labels indicate the transitions for which only one of the frequency-switching data have been used (FS10 corresponds to a throw of 10 MHz).