Line intensity predictions for different isobaric PDR models. Calculations were carried out in a multi-slab Monte Carlo code (Sect. 4) that uses the output of the PDR model. Blue stars show the line intensities observed toward the Bar (corrected by beam dilution). Left panel: SH⁺ emission models for PDRs of different P_th values and α = 5°. Right panel: SH and H₂S (adopting anOTP ratio of 3) emission from: high E_b (magenta squares), low E_b (gray triangles), and gas-phase (cyan circles) PDR models, all with P_th / k = 2 × 10⁸ K cm⁻³. Upper limit intensity predictions are for a PDR with an inclination angle of α = 5° with respectto a edge-on geometry. Lower limit intensities refer to a face-on PDR model.