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tokens: general for the other hydrogenated PAHs. It is also worth noting that the absence of bands at 3.51 and 3.56 μ m is characteristic of hydrogenated PAHs in which extra H atoms are located by pairs in different parts of the PAH (isomers a and e of Figure 5 and the lower spectrum in Figures 6 and 7 , which include the most stable hydrogenated PAHs predicted at the DFT level). Figure 6. Convoluted theoretical harmonic spectra of four stable isomers of C 54 H 18+12 . Isomers are schematically depicted as an inset. Bands located around 3.51 and 3.56 μ m are indicated by orange and green arrows, respectively. The corresponding H atoms that mostly contribute to those bands are identified with the same colors. Energy differences ( E rel ) correspond to the DFT values. Figure 7. Convoluted theoretical harmonic spectra of four stable isomers of C 96 H 24+10 . Isomers are schematically depicted as an inset. Bands located around 3.51 and 3.56 μ m are indicated by orange and green arrows, respectively. The corresponding H atoms that mostly contribute to those bands are identified with the same colors. Energy differences ( E rel ) correspond to the DFT values. 4. Astrophysical Implications Hydrogenated PAH molecules have been experimentally and theoretically studied in their neutral and cationic forms (Thrower et al. 2012 ; Klærke et al. 2013 ; Cazaux et al. 2016 , 2019 ; Jensen et al. 2019 ; Campisi et al. 2020 ). It has been demonstrated that specific isomeric forms are more abundant than others but that hydrogenation on the different positions (secondary and tertiary) occurs. For example, in the case of neutral coronene, the preferred isomeric forms of 2, 4, and 6 H atoms of the main and alternative sequences of hydrogenation (Jensen et al. 2019 ) are among the most stable isomers shown in Figure 3 . The structures with six additional H atoms previously found (isomers b and d) but also others found in this work (isomers c, f, and g) of Figure 3 are already hydrogenated in tertiary positions, therefore showing that even for low degrees of hydrogenation, tertiary positions are hydrogenated. The conditions in some regions of the ISM, for instance at the surface of PDRs, cause hydrogenated PAHs to become ionized, showing stable structures that are different from those of their neutral counterparts (Cazaux et al. 2019 ). In addition, it has been shown that H atoms attached to cationic PAHs can roam over the peripheral carbon atoms producing a “scrambling” of the different isomers upon absorption of interstellar FUV photons (Wiersma et al. 2020 ). Thus, although not all possible isomers are going to contribute equally to spectral features in the ISM, it is still under study which are the different isomers that contribute depending on the reactions that can take place under the particular conditions of the ISM. If “scrambling” of H atoms inside PAHs is a feasible process, it can be expected that the most stable isomers may have strong contributions to the