STRUCTURE OF A 50 MOL KG-1 AQUEOUS-SOLUTION OF AMMONIUM-NITRATE AT 373-K BY THE ISOTOPIC DIFFERENCE METHOD OF NEUTRON-DIFFRACTION

A neutron diffraction study of a 50 mol kg-1 aqueous solution of deuterated ammonium nitrate [ca. 1: 1 molecular ratio of D2O: N(1)D4N(2)O3 which is the saturation solubility at ca. 70-degrees-C] was carried out at 100-degrees-C. The first- and second-order isotopic difference methods of neutron diffraction were applied to the nitrogen nuclei of both the ammonium and nitrate ions. The results derived from the total and first-order difference diffraction functions show the existence of stable ND4+ and NO3- ions in the solution. Structural information concerning the ammonium ion-water and nitrate ion-water coordination was obtained from the first-order differences, and the results indicate a relatively weak hydration shell for these ions. A calculation of the second order difference function enabled the determination of the 'cross' pair radial distribution function g(N(1)N(2))(r) from which it was concluded that the nearest-neighbour N(1)-N(2) distance increases significantly on the addition of D2O to ND4NO3.