Spectra of the CCH (N = 3,2, J = 5/2–3/2, F = 2–2; red) and CH₃OH (5₀ –4₀ A; blue)lines observed with the IRAM-30 m telescope towards six sources of the sample that show well-constrained line profiles suitable for the analysis (see Sect. 5.1) and for which 1mm data are available (see Table 2). For the purposes of visibility, the spectra of CCH has been increased by various scale factors in order to match the size of the CH₃ OH lines.