Electric nuclear quadrupole coupling reveals dissociation of HCl with a few water molecules.

Xie, Fan; Tikhonov, Denis S; Schnell, Melanie · Science · 2024

basic_science · Level V

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Abstract

Investigating the dissociation of acids in the presence of a limited number of water molecules is crucial for understanding various elementary chemical processes. In our study, focusing on HCl(H<sub>2</sub>O)<i><sub>n</sub></i> clusters (where HCl is hydrogen chloride and H<sub>2</sub>O is water) formed in a cold and isolated jet expansion, we used the nuclear quadrupole coupling tensor obtained through rotational spectroscopy to decipher the nature of the hydrogen-chlorine (H-Cl) chemical bond in a microaqueous environment. For <i>n</i> = 1 to 4, the H-Cl bond is covalent. At <i>n</i> = 5 and 7, the contact ion pair of H<sub>3</sub>O<sup>+</sup>Cl<sup>-</sup> is spontaneously formed within the hydrogen bond networks of book and cube acid-water clusters, respectively.