Spectral comparison between PN, SiO, and SO. The PN J = 2−1 spectra (grey histogram) extracted from regions 1 and 2 in Fig. 1 are superimposed on SiO J = 2−1 (red histograms), SO N = 2-1(2) (magenta histograms), SO N = 3−2 (blue histograms), ²⁹SiO J = 2-1 (orange histograms), ³⁴SO N = 2−1(2) (purple histograms), and ³⁴SO N = 3-2 (green histograms) extracted from the same regions. The PN line intensity scale has been appropriately multiplied to perform a consistent spectral comparison with SiO and SO. In each plot, the white vertical bars are the theoretical positions in velocity of the PN J = 2−1 hyperfine components (Table 1), with the strongest one being at the systemic velocity of 96.5 km s⁻¹.