Rotational diagrams for the observed molecules in IRC +10216. For lines with hfs, all observed components have been taken into account. The circles with error bars are from our Effelsberg-100 m observations, where in addition to uncertainties in the fit to the integrated line intensities, a calibration error of 20% has also been included. Filled and open symbols indicate signal-to-noise ratios that are larger than or less than five, respectively. The triangles without error bars are obtained from Kawaguchi et al. (1995). The pentagrams with error bars for C₈H are obtained from Remijan et al. (2007), and the squares for C₃N are from He et al. (2008). Their values have been corrected for beam dilution. The molecules and their corresponding rotational temperatures, obtained from unweighted linear fits, are given in the upper right corner of each panel. Black dashed lines represent linear least-squares fit to the rotational diagram accounting for data presented by filled symbols, and the black dot-dashed lines represent the fit when the open circles are included. The red and blue dashed lines represent fits for the para and ortho states of NH₃ and c-C₃H₂ and the and state of l-C₅H and C₆H, respectively. Specifically for NH₃, the red dashed line shows the fit to the (J,K) = (1, 1) and (2, 2) para-lines, the blue dashed line uses the resulting excitation temperature (39.1 K) and the ortho-(3, 3) line, the dotted red line represents a fit to the para-(1, 1), (2, 2), and (4, 4) transitions and the blue dotted line fits the ortho-(3, 3) and (6, 6) transitions.