Radial profiles of gaseous fractional abundances of H₂O, O₂, O, and OH in NGC 1333-IRAS 4A envelope models. The yellow solid lines and scarlet dash-dotted lines show the radial profiles of our standard model calculations for values of central star X-ray luminosities L_X = 10²⁸ and 10³² erg s⁻¹, respectively (see also Figs. 3, 5, and 6). The orange dashed double-dotted lines and red dotted lines show those of our test calculations assuming that the product of H₂O photodissociation is 100% atomic oxygen, unlike our standard model (100% OH) (see also Fig. H.1). The orange double-dashed dotted lines and brown dashed lines show those of our test calculations assuming the smaller E_des (j) for atomic oxygen (=800 K) than that in our fiducial model (=1660 K) (see also Fig. H.2). In the top left panel, the observational best-fit H₂O gas abundance profile obtained in van Dishoeck et al. (2021) is overplotted with the black solid line (see also Fig. 10). In the top right panel the three model O₂ gas abundance profiles obtained in Yıldız et al. (2013) are overplotted (see also Fig. 10).