Continuum-subtracted Herschel-PACS spectra of HD 100546 around the CH⁺J = 6−5, 4−3, 3−2, 2−1 (DIGIT data), and J = 5−4 (GASPS and DIGIT data) lines. The 3σ statistical error levels do not include the 30% calibration uncertainty. A rotational diagram using those transitions is plotted in the lower-right panel. The errors in the diagram are the quadratic sum of all the statistical and calibration errors (). Blended lines are considered as upper limits (red filled dots).