C₂H N = 1−0, 2−1, 3−2, 4−3, 6−5, 7−6, 8−7, and 9−8 rotational transitions in IRC +10 216’s envelope as observed with the IRAM 30 m telescope and Herschel/HIFI. The fine structure components are labelled with the respective J-transitions in the top of each panel, while the hyperfine components are indicated with vertical dotted lines. For the sake of clarity, we omitted the components that are too weak to be detected. See Sect. 4 for details on the spectroscopic structure of C₂H. Additionally observed features related to other molecules are also identified.