SiC₆ lines observed in this work, with the fit for them in red. Black dots correspond to lines with no critical blending from other species while open dots identify lines heavily blended. The dashed magenta curves represent the overall fit for all lines according to the parameters given in Table 1. The bold red curves correspond to the contribution of the SiC₆ lines alone. The rms or σ values given for each spectrum in dark blue are calculated from the channels, with no signal in the fitted spectrum. The best-fit rotational diagrams using only the not heavily blended SiC₆ rotational transitions are shown separately as solid and dashed lines, respectively, in the bottom panel.