o-H₂D⁺ spectra for half the sources of our sample (cyan). In each panel, the source name is shown on the left in red, while the integrated main-beam temperature, ∫_chT_mb dυ, and rms (irms) are on the right in black. The green dotted line represents the 1σ noise levels in T_mb. The frequency and velocity axes are reported and cut around the line, while the intensity axis is fixed to the highest T_mb detected (observed in G14.23–0.51). The black dashed lines indicate the v_lsr of each source derived from the C¹⁷O J = 3–2 and the NH₃ (1, 1) lines (see Table 1). The model obtained with MCWeed is superimposed in red.