Neutron Diffraction Study of Aqueous Ionic Solutions. I. Aqueous Solutions of Lithium Chloride and Caesium Chloride

The structure factors Sm(Q) for aqueous solutions of LiCl and CsCl at room temperature, including those for heavy water, have been determined by means of the time-of-flight (TOF) neutron diffraction method using an electron linear accelerator (LINAC). Analysis of the diffraction data has been carried out for the aqueous ionic solutions as well as for pure heavy water. The following results were obtained with respect to the structure of the nearest hydration shell: (a) the coordination numbers are 4 for Li+ and 6 for Cl− in the LiCl solution, and 8 for Cs+ and 6 for Cl− in the CsCl solution, (b) the average ion-oxygen distances are 1.90±0.05 Å for Li+, 2.95±0.10 Å for Cs+ and 3.10±0.05 Å for Cl−, and (c) around cations water molecules take the configuration to orient the axis of one of two lone-pair hybrids on a straight line joining an oxygen atom and a cation.