Radiation fields and H₂O photodissociation cross section adopted in this work. Top: spectral shape of the radiation fields as a function of wavelength. The radiation fields have been scaled to agree with the integrated energy-intensity of the Draine (1978) radiation field between 91.2 and 200 nm, that is, 2.6 × 10⁻⁶ W m⁻². Bottom: photodissociation cross section of H₂O producing OH adopted in this work (black) and the extension to 911 Å (gray). The features due to photodissociation through the Ã, , , and states of H₂O are also indicated.