The structure of an aqueous ammonium chloride solution

X-ray measurements have been performed on a 2 molal NH4 Cl solution at 25 °C. The scattering data have been evaluated with the first neighbor model (FNM). These results are compared with molecular dynamics (MD) simulations where the ST2 model for water is employed. The NH4+ is described by a rigid tetrahedron with point charges at the positions of the hydrogen atoms and the Cl− by a Lennard-Jones sphere with an elementary charge at the center. Good agrement has been found between the measurements and the simulation. Contrary to previous results the nearest neighbor distance for NH4+–water is found to be significantly different from the one for water–water. The structure of the solvent described by the nearest neighbor distance and its root mean square deviation is in the limits of error the same as in pure water and significantly different from the solvent structure in alkali halide solutions.