Notes. ^(a) Rest frequencies taken from the Cologne Database for Molecular Spectroscopy, CDMS (Müller et al. 2005; Endres et al. 2016). Original sources of spectroscopic data: C¹⁷O, Klapper et al. (2003); CO, Winnewisser et al. (1997); H¹³CN, Cazzoli & Puzzarini (2005); H₂CO and H₂ ¹³CO, Cornet & Winnewisser (1980); C³⁴S Gottlieb et al. (2003); SiO and ²⁹SiO, Müller et al. (2013); C₂H, Padovani et al. (2009). ^(b)Critical density is calculated as the ratio of the Einstein A coefficient and the collision rate at a temperature of 100 K, which are accessed through the LAMDA database (Schöier et al. 2005), with the following original sources: CO (adopting o-H₂ as dominant collision partner), Yang et al. (2010); H¹³CN, Dumouchel et al. (2010) for main isotopologue; H₂CO and adopting identical rates for H₂ ¹³CO, Wiesenfeld & Faure (2013); C³⁴S adopting rates for the main isotopologue C³²S, Lique et al. (2006); SiO and adopting identical rates for ²⁹SiO, Dayou & Balança (2006); C₂H, Spielfiedel et al. (2012). ^(c)source A and source B are abbreviated as “A” and “B”; “PA” denotes position angle east of north, following Fig. 1. ^(d) The hyperfine splitting of C¹⁷O 3–2 and H¹³CN 4–3 is discussed in Appendix A. ^(e)For ¹²C¹⁶O, we study morphological features using only velocity channels at | V_lsr – v_systemic | > 5 km s⁻¹, as shown in Fig. 4. ^(f) The rest frequency for C₂H 4_7∕2 – 3_5∕2 is the average of the tabulated rest frequencies for the individual hyperfine components, F = 4–3 at 349.39928 GHz and F = 3–2 at 349.40067 GHz.