Normalized intensity profiles of four species towards L1551-IRS5. The spectra of CH₃OH in green and c-C₃H₂ in pink in the upper panel are obtained after stacking the detected transitions (see Fig. 5). The spectra of H₂S in blue and OCS in red in the lower panel are transitions 2_2,0–2_1,1 and 19–18, respectively (see Fig. A.4). The dashed and dash-dotted lines represent the systemic velocities of the southernprotostar (4.5 km s⁻¹) and the northern protostar (7.5 km s⁻¹), respectively (Bianchi et al. 2020), while the dotted line represents the systemic velocity of the circumbinary envelope (6.4 km s⁻¹) measured using the C¹⁸O 2–1 line (this work).