Total spectra and simultaneous fit of the CO(1–0), CN(1–0), HNC(1–0), HCO⁺(1–0), HCN(1–0), CO(2–1), HCN(2–1), CO(3–2), and HCN(3–2) molecular lines in Mrk 231. Overlaid on the data, we show the individual Gaussians employed in the simultaneous fit (up to three components for each line, red dashed curves) and the total best-fit curve (blue solid lines). Only the fainter HC₃N(10–9) line was fitted by a single Gaussian with unconstrained velocity and width. The rms values per spectral channel are 1.7 mJy per δv = 14 km s⁻¹ (CO(1–0)); 2.3 mJy per δv = 43 km s⁻¹ (CN(1–0)); 1.7 mJy per δv = 40 km s⁻¹ (HNC(1–0)); 1.4 mJy per δv = 70 km s⁻¹ (HCO⁺ and HCN(1–0)); 8 mJy per δv = 26 km s⁻¹ (CO(2–1)); 1.2 mJy per δv = 60 km s⁻¹ (HCN(2–1)); 26 mJy per δv = 18 km s⁻¹ (CO(3–2)); and 5 mJy per δv = 47 km s⁻¹ (HCN(3–2)).