Infrared spectra of OH following H₂O photodissociation at two photon wavelengths computed with GROSBETA. Top: at λ = 166 nm, H₂O dissociating via its first excited à electronic state and producing rotationally cold OH. The OH infrared spectrum is dominated by far-IR lines excited by collisions and IR radiative pumping. Bottom: at λ = 121.6 nm, H₂O dissociating via its second excited electronic state and producing rotationally hot OH. OH lines in the mid-IR with N_up = 20–45 trace H₂O photodissociation through this electronic state. The density, temperature of the background radiation and kinetic temperature are fixed to their fiducial values (see Table 1) and Φ = 10¹⁰ cm⁻² s⁻¹. In this figure, all lines are colored red, even if coming from cross-ladder and intra-ladder transitions.