Velocity-integrated PdBI contour maps obtained towards OMC-2 FIR 4, overlaid on the naturally weighted continuum map (grey scale). The bottom-left ellipse in each panel represents the beam size. Left: CH₃OH(3, 1, +0 – 2, 1, +0) (black) and C³⁴S(3–2) (magenta). Centre: DCN(2–1) (black) and DCO⁺(2–1) (magenta). All the contours start at 3σ and increase by steps of 3σ. The 1σ rms values are 0.16, 0.14, 0.17, and 0.08 Jy beam^-1 km s^-1, respectively for the CH₃OH, C³⁴S(3–2), DCN(2–1), and DCO⁺(2–1) integrated maps. Right: Polygons representing the three differentiated components, main, west, and south (see text), used to extract average spectra. The white crosses mark the positions of the three sources identified in this work (see Table 4).