Spitzer/IRS PAH ratios for the circumnuclear regions of the Seyfert galaxies in our sample (circles) except for those in highly inclined hosts (see text). For NGC 3081 and NGC 7213, we only obtained an upper limit for the 11.23 μm PAH. We assumed that its flux is approximately 1/4 of that of the 11.33 μm PAH, as in other type 1 Seyfert galaxies. The symbols are color-coded with the nuclear H₂ column density. The plotted error bar in each direction represents the effect of a 10% uncertainty in the 7.7 μm PAH complex flux on the measured PAH ratios. The lines are PAH model tracks (Rigopoulou et al., in prep.) for molecules in a Galaxy-like ISRF (solid gray lines), an intense ISRF equivalent to ×10 000 the Galaxy (dashed red line), and numbers of carbon atoms from N_C = 20 to N_C = 400. For the Galaxy-like ISRF, the top line is for neutral PAHs and the bottom line for a 40% fraction of ionized PAHs. The number of carbon atoms for the PAH molecules increases from right to left.