Water Attachment onto Size-Selected Cationic Hydroxy–Pyrene Clusters

Abstract

We study the attachment of a single water molecule colliding with cationic clusters of hydroxypyrene (PyOH)─a medium-sized hydroxylated polycyclic aromatic hydrocarbon (OH-PAH). The (PyOH)_n⁺ clusters (n = 2–6) were generated using a cryogenic molecular cluster source. The attachment rates are measured as a function of collision energy and initial cluster temperature. To rationalize the experimental results, we use a model that accounts for the dissociation rates of the water molecule in [(PyOH)_nH₂O]⁺ complexes to estimate the survival probability of these species. The derived binding energies range from ∼0.5 to 0.4 eV, decreasing with cluster size. By comparing our results with a previous study on pyrene clusters, we highlight the key role of charge combined with the hydroxyl function in enhancing the stability of [(PyOH)_nH₂O]⁺ complexes at higher temperatures. These findings add a new piece to the chemical network driving the physico-chemical evolution of PAHs and their role in planet-forming regions and exoplanetary atmospheres.