Schematic summarizing the results of the time evolution of the integrated intensities for the different models: size of the ionized cavity and density profile (top panel), density at the ionization front (second panel), initial abidances (third panel) and cut-off density (bottom panel). Lines with the integrated intensity I_int > 100 are represented in green, 10 < I_int < 100 in yellow, 1 < I_int < 10 in orange and I_int < 1 K km s⁻¹ in red. Undetected lines, with integrated intensities lower than the detectability threshold of 5 × 10⁻² K km s⁻¹, are represented in gray.