Flipping Kinetics of the Water Trimer on Acenaphthylene: Persistence of a Highly Dipolar ddd Configuration at Interstellar Temperatures

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.