Infrared Spectroscopy of [H₂O–N₂O]⁺-(H₂O)_n (n = 1 and 2): Microhydration Effects on the Hemibond

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The hemibond, a nonclassical covalent bond involving three electrons shared between two centers, has attracted considerable attention due to its significance in radiation chemistry. Water radical cation clusters, [H₂O–X]⁺, exhibit two primary bonding motifs: the hemibond and the hydrogen bond. Although hydrogen bond formation typically dominates, recent studies have identified instances of hemibond formation in some systems involving water molecules. This study focuses on the [H₂O–N₂O]⁺ radical cation cluster, a rare system exhibiting hemibond formation. We investigate the stability of this hemibond in [H₂O–N₂O]⁺ against microhydration by employing infrared photodissociation spectroscopy and conducting theoretical calculations on [H₂O–N₂O]⁺-(H₂O)_n (n = 1 and 2). By comparing experimental and simulated spectra, we determined the predominant intermolecular bonding motifs in [H₂O–N₂O]⁺-(H₂O)_n (n = 1 and 2). Our analysis revealed that proton-transferred-type isomers are almost exclusively populated for n = 1 and 2, whereas hemibonded-type isomers are energetically unfavorable. These findings indicate that microhydration disrupts the hemibond and shifts the stable structural motifs.