Non-Covalent Interactions in the Hydrated Clusters of Interstellar Molecules: A Quantum Chemical Exploration

The non-covalent interactions present within the mono-, di-, and tri-hydrated clusters of a few structurally analogous small molecules found in the interstellar medium have been investigated using topology, electrostatic potential, and population-based quantum mechanical tools to critically analyze their characteristics and energetics. Along with the presence of purely electrostatic hydrogen bonding (HB) interactions, the clusters are found to contain HBs with credible covalent characters, further validated by fuzzy atom analysis. Moreover, all the interaction energies were segregated into physically and chemically meaningful constituent terms by means of the absolutely localized molecular orbital formalism which not only shows that the associated HBs are governed by permanent electrostatics (monopolar and multipolar), polarization, charge-transfer, and dispersion forces with their relative contributions varying substantially with the molecules but also identifies Pauli repulsion as a prominent factor in governing the overall energetics of the interaction lines. Finally, thermodynamic analysis has been utilized to show to complex interplay of entropy in the formation of the studied clusters.