Observed transitions of C₅N⁻ in TMC-1. Quantum numbers are indicated at the top right of each panel. The abscissa corresponds to the rest frequency adopting a velocity for the source of 5.83 km s⁻¹ (Cernicharo et al. 2020c). The ordinate is the antenna temperature, corrected for atmospheric and telescope losses, in mK. Blank channels correspond to negative features produced when folding the frequency-switched data. The red line shows the modelled spectra for these lines (see App. E).