Hydrogenation ratio for different G₀/n(H) values. The ratios derived from circumcoronene derivatives are shown in blue, while those from circumcircumcoronene derivatives are shown in red. We have assumed a gas temperature of 50 K, and that the fraction of atomic hydrogen is 10% that of molecular hydrogen, in order to model more shielded environments. The 3.4/3.3 ratio traces the superhydrogenation level of the PAHs as the 3.4 μm band is related to the stretching modes of the pair of CH₂ complexes within the same ring (which are duo rings for the coronene family). Observed 3.4/3.3 ratios in NGC 7023 range between 0.028 and 0.13, starting from the cavity and going into the NW PDR region, where G₀ is expected to vary from 7000–150 (Pilleri et al. 2015). We see that these ratios can be achieved with superhydrogenated species but for G₀/n(H) ratios of 0.002–0.006, which is lower than what is expected in the NW PDR of NGC 7023.