Smoothed C¹⁷O(2−1), H¹³CO⁺(3−2), DCO⁺(3−2), N₂H⁺(3−2), and N₂D⁺(3−2) spectra (top to bottom) towards the clumps (left to right). Overlaid on the spectra are the hf-structure fits. The relative velocities of each individual hf components in each observed transition are labelled with a short bar on the spectra towards I18102 MM1; these are also shown in the C¹⁷O and N₂H⁺ spectra towards G015.31 MM3. The red vertical line on the N₂D⁺ spectrum towards G015.31 MM3 shows the v_LSR = 30.81 km s^-1 of the clump as measured from N₂H⁺(1 − 0) by SSK08. Note that N₂H⁺(3−2) observations were carried out only towards three sources and that N₂D⁺(3−2) was not detected towards G015.31 MM3, I18182 MM2, and J18364 SMM1.