This is a theoretical study aiming to understand molecular processes with water clusters, which can be useful for the detection of polycyclic aromatic hydrocarbons (PAHs) in space. From structural features, multiple-body energy fragmentation, vibrational spectra, and kinetics of hydrogen bonding, we investigate the effects of complexation between acenapththylene and a cyclic water trimer. Our results suggest that the trimer may be anchoring on the aromatic plane of the molecule in an unconventional ddd configuration (i.e., with three O–H bonds pointing down “d” to the molecular plane). By calculating a structural cooperativity parameter and the multiple-body energy terms for the complexes fragmentation, the ddd configuration results in a greater structural mobility of hydrogen bonding. The flipping kinetics indicates the persistence of this unconventional configuration of the water trimer for an energetically viable intermolecular complex at T ≤ 30 K. The structural changes of the complexes imply correlated changes in their IR/Raman spectra. Our results may arouse interest for investigating cold interstellar processes of PAHs in the presence of water aggregates. Moreover, the study may contribute to elucidate specific vibrational emission features of hydrated PAHs at low-temperature experiments.

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We investigate the photoionization pathways of naphthalene, 1-cyanonaphthalene, and 2-cyanonaphthalene upon complexation with the water dimer, aiming to understand the photodissociation process under conditions of the interstellar medium (ISM). We analyze the intermolecular bonding pattern, equilibrium rotational properties, energy complexation, far-IR spectra, and ionic trends of the possible photoproducts using dispersion-corrected density functional theory (DFT-D) and timedependent DFT (TD-DFT). For the different configurations, we evaluate the possible charge-transfer (CT) excitations near the photoionization limit. Our results indicate that, in high-radiation regions of the ISM (>8.0 eV), CT excitations occur from localized occupied molecular orbitals (MOs) in the aromatic molecules to mixed unoccupied MOs in the complexes, favoring cationic aromatic species in these conditions. We notice that the photoabsorption spectra depend on the type of intermolecular interaction (H-bonds or O−H•••π bonds) in the complexes, as well as the presence and position (1 or 2) of the cyano-functional group in naphthalene. For hydrated naphthalene, the O−H•••π complexes assume a more relevant role for photodissociation. In the case of the cyano-substituted derivatives, the H-bonded structures are more favorable to be considered as prereactive models. However, the cyano group at position 2 indicates that CT excitations toward the water dimer are more likely to occur.

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