Radiative transfer results (in red) overlaid to the observations (in black) for all the targeted transition obtained with the chemical model with initial cloud evolution to set the initial conditions, obtained at t = 10⁶ yr (see Sect. 4.4). The model implements constant ζ₂ equal to the fiducial model (ζ₂ = 1.3 × 10⁻¹⁷ s⁻¹). The top row shows the DCO⁺ lines, while the bottom row presents the two N₂H⁺ transitions and the HC¹⁸O⁺ (1-0) line, from left to right. The corresponding panels for N₂D⁺ are presented in Fig. 10. The used f_corr value is shown on top of each panel.