The nature of acids in aqueous media is fundamental to many aspects of chemistry and this is why halide-acid dissociation has been extensively studied in various types of aqueous environments both from the experimental as well as from the theoretical points of view. Some of these studies address HCl hydration at the liquid-air interphase but there is a large number of investigations where microsolvation is considered either by water clusters and very recently also by 35 μm water microjets. Acids are fundamentally defined by their ability to transfer a proton to water, but this seemingly simple process can be quite complex and it is well known to be highly dependent on the solvation conditions. In this contribution we present the results from a Born-Oppenheimer Molecular Dynamics (BOMD) study of a HCl molecule surrounded by 40 water molecules, which allows to refer the excess proton H* and the protonated oxygen O* to the location of the chloride anion Cl- thus also permitting a direct comparison to data obtained from neutron diffraction experiments. A very good agreement of the radial distribution functions was found, which shows the adequacy of BOMD of small gas phase clusters to approach the aqueous solution of small molecules and validates the findings of this study with regard to the dynamics of the diffusion of O* and the faster dynamics of the excess proton: the Grotthus hoping mechanism.

Proton hydration in gas phase clusters: Born–Oppenheimer molecular dynamics hybrid DFT study of HCl in a water nanodroplet

2019 Fall National Meeting

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