Observed spectrum of N-ethylformamide between 110.1 and 115.9 GHz. The total observing time per W sub-band was 59 h. The observing procedure was frequency switching with a throw of 25 MHz. The pressure in the chamber was 3 × 10⁻³ mbar. The intensity scale is in K and the frequency scale in MHz. The different panels show different magnifications of the data of the upper panel. The two lines at the bottom have a linewidth of ≃0.4 MHz. The 19_1, 19–18_0, 18 transition shows a shoulder at lower frequencies produced by a line arising from one of the low-lying vibrationally excited states or from the conformers trans-ap or cis-ac (the expected hyperfine splitting for this transition is ≃15 kHz).