Infrared spectra of OH depending on the column density of H₂O photodissociated per unit time Φ and on N(OH) computed with GROSBETA for a Lyα UV radiation field. The density, temperature of the background radiation and kinetic temperature are fixed to their fiducial values (see Table 1). Following the color code used in Fig. 1, intra-ladder rotational lines are in red and blue and cross-ladder lines are in orange and green. Λ-doubling lines are too weak to appear here. The weak mid-IR lines lying in the range ~ 10–13 μm are intra-ladder rotational lines within the OH(X)(v = 1) state. The N_up rotational number of the upper energy level is indicated for selected lines.