Top: vertical cut at r = 0.15 au showing the abundances of several key atoms and molecules. Middle: Irradiation conditions in this vertical cut, with $G_0^{{\mathrm{H}}_2\mathrm{O}\mathrm{s}\mathrm{h}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d}}$ showing the UV field attenuated by water absorption (water shielding). The gray line G₀ indicates what the UV field would be without the water UV shielding. Bottom: gas and dust temperature, with the gas density n_H in blue. Water UV shielding allows C₂H₂ to be abundant much higher in the disk by suppressing UV photodissociation.