Spectral features of the J = 4 − 3 (left), 3 − 2 (center) and 2 − 1 (right) transitions from three of the isotopologues of CCH detected in the survey. Red curves shows the LTE model best fits. Contributions by other species is almost negligible for most transitions according to the global LTE model from the full survey (see Sect. 4.3.2). However we note that the observed profile of ¹³CCH 4−3, not following the CCH LTE model and not accounted for by emission from other species, was not used in the fit.