Mopra average spectrum of HCO⁺ 1–0 towards Sgr B2(N), extracted from the imaging survey of Jones et al. (2008) after excluding pixels with absorption (see Fig. 22). The black and blue spectra were obtained with the broad-band and narrow-band backends, respectively. They are displayed in scale. The purple spectrum is the EMoCA spectrum of H¹³CO⁺ 1–0 towards K4 in brightness temperature scale. The feature between −280 and −210 km s⁻¹ is caused by SiO in the envelope of Sgr B2. The dashed line marks the channel that corresponds to a ¹³CO emission peak in Fig. 24.