The structure of molten ammonium nitrate by isotopic difference method of neutron diffraction

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Abstract
A neutron diffraction study of the atomic structure of deuterated molten ammonium nitrate (N(1)D4N(2)O3) was carried out at 453 K. The first and second order isotopic difference methods of neutron diffraction were applied to the nitrogen nuclei of the ammonium and nitrate ions. The results of the total and the first order differences demonstrate the existence of stable ND+ 4 and NO- 3 ions in the melt. The ND+ 4 ions conform to a tetrahedral geometry and the NO- 3 ions retain a D 3h symmetry arising from a triangular geometry. The second order difference enabled the determination of the ‘cross’ pair distribution function g N(1)N(2)(r), from which it was concluded that the crystal structure relaxes significantly on melting.