HIFI observations of the C₃ lines in DR21(OH). The spectra are corrected for the DSB continuum and normalized to the SSB continuum level. The Q(2), P(4), and P(10) spectra are shifted consecutively by +0.5, so that the plots do not overlap. The red line shows the simultaneous fit with three Gaussian velocity components (at −0.7, −2.9, and −4.2 km s^-1). Note that the third component is only detected above the noise in Q(4) and P(4). The “negative” absorption bumps at this velocity fitted in Q(2) and P(10) are within the noise.