Hydrogenation state of circumcoronene (C₅₄H₁₈, red) and circumovalene (C₆₆H₂₀, black) as a function of the intensity of the UV radiation field G₀ in Habing units and the local density n_H. The lines labelled with 0.1 (respectively 0.5, 0.9) show the points for which 10% (respectively 50%, 90%) of the species are totally dehydrogenated. For coronene, only the blue line labelled with 0.995 where 99.5% of coronene is fully dehydrogenated is represented, which is the dominant state of coronene for all the conditions spanned here.