Normalized spectral intervals between the sub-peaks in the profiles of several C₂ -DIBs as a functionof the C₂-based kinetic temperature (see text) of each target. Uncertainties on the intervals can be deduced visually from the drawn profiles in Figs. 3–7, and are on the order of the data point dispersion. The dashed line is a linear fit to the average over the five different DIBs. The size of the marker indicates the reliability of the sub-peak interval determination, again visually determined from the quoted figures. The three targets used for the co-addition of the DIB profiles are marked by arrows.