Normalized photon intensity of the OH(X²Π)(v = 0) intra-ladder mid-IR lines as a function of the quantum number of the upper energy level N_up. The intensities are computed for the fiducial values of the parameters (see Table 1) and normalized by the column density of water photodissociated via its state (see Eq. (18)). Circle and triangle markers correspond to lines belonging to the Ω = 1∕2 and Ω = 3∕2 ladders, respectively. Λ-doublets are indiscernible in this plot. In this regime, rotational levels are only populated by the radiative cascade of OH photofragments and , depends only on the shape of the adopted radiation field.