Influence of concentration and anion size on hydration of H+ Ions and water structure

Neutron diffraction experiments with hydrogen isotope substitution onaqueous solutions of HCl and HBr have been performed at concentrationsranging from 1:17 to 1:83 Solute per water molecules, at ambientconditions. Data are analyzed using the empirical potential structurerefinement technique in order to extract information on both the ionhydration shells and the microscopic structure of the solvent. It isfound that the influence of these solutes on the water structure isless concentration dependent than that of salts or hydroxides. Moreoverprotons readily form a strong H-bond with a water molecule uponsolvation, at all proportions. The majority of them is also bonded viaa longer bond to another water molecule, giving a prepeak in theg(OwOw). At high solute concentration, the second water molecule may beSubstituted by the counterion. In particular at solute concentrationsof the order of 1:17 or higher, all protons have an anion within adistance of 4.5 angstrom