Isobaric PDR model of the Orion Bar (G₀ ≃2 × 10⁴, P_th/k_B = 2 × 10⁸ cm⁻³ K) showing abundance profiles with respect to H nuclei. The gray dotted curve shows f₇, the fraction of H₂(v > 7) with respect to the ground (right axis gray scale). Solid curves refer to a model using state-specific reaction rates for reaction S (³P) + H₂ (v) → SH + H, whereas dashed curves refer to a model using the thermal rate.