The structure around nitrate ions in concentrated aqueous solutions

The first-order-difference method of neutron diffraction has been applied to a 7.8 molal aqueous solution of sodium nitrate in which isotopic substitutions were made on the nitrate ion. The intramolecular distance is found to be 1.23+or-0.02 AA. There are 1.3+or-0.2 water molecules coordinated axially to the nitrate ion with r_ND and R_NO values of 2.05+or-0.02 and 2.65+or-0.10 AA respectively. A model for the longer-range structures is proposed.