Observed lines of CH₃CH₂CN in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s⁻¹. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top left corner of each panel. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.2. Blanked channels correspond to negative features produced in the folding of the frequency-switching data.