Assorted quantities calculated in the PDR model of the Orion Bar plotted as a function of A_V. The solid lines refer to the model including H₂ state-specific rate coefficients for reaction (1), and the dashed lines to the reference model in which a thermal rate coefficient is used for reaction (1). Top right panel: contribution of each vibrational state of H₂ to the total rate coefficient of the O + H₂ reaction, expressed as f(H₂(v)) × k(O + H₂ (v)), where f(H₂(v)) is the fractional population of H₂ in the vibrational state v. Bottom right panel: contribution of the three main gas-phase reactions of formation of OH, expressed as a percentage of the total OH formation rate.