Neutron Diffraction Study on the Structure of Highly Concentrated Aqueous LiBr Solutions

Neutron diffraction measurements have been carried out on aqueous solutions with 20 mol% lithium bromide. The isotopic substitution technique was applied to lithium ions and hydrogen atoms of the water molecule. The measured results were used to determine the partial pair distribution functions gLiO(r), gLiH(r), and gHH(r). The Li+···water molecule configuration is characterized by the intermolecular distances rLiO = 1.96 ± 0.02 Å and rLiH = 2.60 ± 0.02 Å, and the tilt angle between the Li+···O axis and the molecular plane of water molecule, φ = 27 ± 10°. The mean coordination number of water molecules around Li+ is computed to be 3.9 ± 0.5. The hydrogen–hydrogen pair correlation function gHH(r) obtained from observed cross sections of these solutions with different isotopic compositions exhibits that each hydrogen atom in a given water molecule is surrounded with 3.7 ± 0.5 hydrogen atoms of neighboring molecules located at rHH = 2.65 ± 0.05 Å. The hydrogen bond among water molecules may be considered to be markedly destroyed in the present concentrated LiBr solution, compared with that in pure liquid water.