Surface curvature effects in neutral and protonated water clusters: insights from DFT and energy decomposition analysis†

Abstract

Polycyclic aromatic hydrocarbons (PAHs), abundant in interstellar cold dust grains, exhibit distinct interactions with neutral and cationic water clusters depending on carbon surface curvature. To investigate these effects, we have performed quantum-chemical calculations on the complexation of (H2O)5 (neutral water pentamer), H3O⁺(H2O)3 (Eigen-type cation), and H5O2⁺(H2O)2 (Zundel-type cation) with planar coronene and curved corannulene. Our results reveal that the relative stability of neutral and cationic clusters is governed by both the number of O–H⋯π bonds and the concavity of the surface. For example, Eigen-type cation stabilizes in planar coronene and convex corannulene, while Zundel-type cation is slightly stabilized on concave corannulene. Infrared absorption features, including shifts and splittings of proton-transfer and O–H stretch modes, are assigned to these complexes, providing spectroscopic signatures of curvature-dependent interactions.