Results of our fiducial model with Pth/k =10⁸ K cm^–3 and . (Top panel) Gas density and gas and dust temperature as a function of visual extinction. The size of the small (big) grains is 10^–7 cm (3.10^–5 cm). (Bottom panel) H₂O, OH, and H₂ abundances as a function of visual extinction. H₂O photodissociation rate k (s^–1) is also represented in light gray. The vertical red line shows the position of the H⁰/H₂ transition. The local UV field intensity is given at seven different positions at the top of the graph.