Example spectra for the model in Fig. 2. Each panel reports the spectra of the molecule and the transitions indicated in the legend. The spectra are convoluted with a telescope beam, as discussed in the main text. We note that the y-axis is scaled to the value at the top of the panel, e.g., C¹⁸O temperature is scaled to 10⁻¹. All the spectra are calculated with a −2 to +2 km s⁻¹ bandwidth range and 128 channels, except for N₂H⁺, N₂D⁺, and HCN where the bandwidth is calculated by LOC to take into account the hyperfine structure of these molecules, but interpolated to use 128 channels. We also use the spectra centered according to the LOC output (i.e., the position of 0kms⁻¹).