Observed lines of HC₃HCN in TMC-1 from the QUIJOTE line survey (black histogram) and synthetic spectra (red curve) calculated adopting a column density of 2.2  ×  10¹¹ cm⁻². Blanked channels correspond to negative features produced in the folding of the frequency-switching data. For each rotational transition, the most intense hyperfine components are shown. The abscissa corresponds to the rest frequency assuming a local standard of rest velocity of 5.83 km s⁻¹. The ordinate is the antenna temperature in millikelvins.