C₃ 000-000 band in three representative sightlines. Top panel: HD 147889, in addition to harbouring the largest N(C₂), also harbours the largest N(C₃) in our data sample. The transitions are all labelled, including those to the original and the perturbed upper energy levels (the latter are highlighted with asterisks; refer also to Sect. 4.1 and Table 2). Bottom panels: The C₃ band is tentatively detected towards HD 23180, mainly through its piled-up Q branch in the middle. The sightline of HD 161056 contains two velocity components of C₃. The synthetic spectra for the two components are plotted with a positive offset in different colours.