Rotational diagrams of the carbon chains CH₃CCH, CCH, C-C₃H₂, and HC₃N. HC₃N is described by three rotational diagrams showing the three temperatures traced by HC₃N. The first rotational diagram is for the narrow component and low temperature. The two following rotational diagram are the two rotational diagrams for the two temperature components covered with the larger line width. Finally, we show the vibrationally excited state of HC₃N, which is a different entry and represents the column density of the molecule present in this vibrationally excited state.