C₂H and SiN emission. High-signal-to-noise ratio detection of C₂H (3−2) in the PI230 data, plotted at 3.0 MHz (≈3.5 km s⁻¹) spectral resolution. Vertical red lines indicate the position and relative strength of the hyperfine structure components of the rotational transition of C₂H. In red, we overplot a synthetic spectrum of C₂H (3−2) using a “shell” profile as described in the GILDAS/CLASS manual, fitted to the data by eye, using the intrinsic component strengths. In blue we indicate the location of the strongest components of the SiN (N = 6−5) transition; see Fig. B.6 for all detected SiN emission. We mark the rest frequency of SiC₂ (12_0,12−11_0,11) in green.