Normalized photon intensity of the OH(X²Π)(v = 0) intra-ladder mid-IR lines as a function of the rotational number of the upper energy level. The intensities are computed for the fiducial parameters given in Table 1 and for three spectral shapes of the UV field (color coded), and divided by Φ according to Eq. (13). 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. The solid line is the analytical model assuming that the intra-ladder lines within the v = 0 state are produced by the radiative cascade of OH fragments produced in the v = 0 state (Eq. (C.6)). The dotted line is the analytical model that assumes that any OH produced in a vibrational state instantaneously decays toward the ground vibrational state with a negligible change of its rotational number (see Eq. (C.7)).