Gas temperature structure (upper-left panel), PAH average charge (upper-right panel), C⁺ abundance (lower-left panel) and the CO abundance (lower-right panel) for the model with H₀ = 5% and a gas-to-dust-mass ratio of 100. The gap between 100 and 185 AU is not empty but is filled with a very low density gas. The computation of the gas temperature in the low gas density gap is not reliable.