In bulk water, HCl exists as ions with the Cl- anion and the hydrated excess proton. The positive charge is delocalized among the solvating water molecules and the excess proton can hop between water molecules via the Grotthuss shuttling mechanism. In order to model this accurately, reactive force-fields are required that allow for changes in bond topology. One such model is MSEVB3.2, which is a multistate empirical valence bond based method. In contrast to the bulk, in the gas phase HCl exists as a covalent compound. Our ab initio/electronic structure investigations of (H2O)n clusters (n=1-22) show that covalent HCl structures are still present at small values of n and even at larges clusters sizes (n=21,22 etc.) one still sees contact ion pairs that are still low in energy. We have modified and re-parameterized the MSEVB3.2 model to incorporate these HCl states. I will present our results on both HCl-water clusters as well as ion-pairing effects at the air-water interface obtained using this modified force-field.

Investigation of ion-pairing and covalent states in hydrated HCl: From clusters to the air-water interface

2019 Fall National Meeting

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