Neutron diffraction and MD studies of LiBr hydrated melts

Abstract Neutron diffraction measurements for H/D isotopically substituted 10, 25 and 33 mol% LiBr hydrated melts and the corresponding MD simulations have been carried out to investigate the intermolecular hydrogen-bonded structure in extremely concentrated aqueous solutions. Observed neutron intermolecular interference terms for the sample solutions with different H/D isotope ratios were combined to deduce partial structure factors, a HH ( Q ), a XH ( Q ) and a XX ( Q ) (X: Li, Br and O), and their Fourier transforms, g HH ( r ), g XH ( r ) and g XX ( r ), respectively. Observed g HH ( r ) and g XH ( r ) for the 10 mol% LiBr solution indicate the well-defined first peak located at r =2.4 and 1.9 A, respectively. The latter 1.9 A peak almost disappears for concentrated 25 and 33 mol% LiBr solutions, implying that the hydrogen-bonded network is completely broken. These results agree well with those obtained from the MD simulation. A gradual shift of the first peak position of the simulated g OO ( r ) towards a longer- r side is observed with increasing LiBr content, which also reflects the collapse of the hydrogen-bonded structure in the solution. The formation of the contact ion pair Li + ⋯Br − , was confirmed for highly concentrated 25 and 33 mol% LiBr solutions.