ANHARMONIC MOTION AND MULTIPOLAR EXPANSION OF THE ELECTRON-DENSITY IN NANO3

NaNO3, R(3) over barc$, a = 5.0701(2) Angstrom, c = 16.822(2) Angstrom, V = 374.4 Angstrom(3), Z = 6. Neutron diffraction: lambda = 0.87013 Angstrom, mu = 0.1 cm(-1), F(000) = 182.1 fm. The intensities are checked for normal and independent distribution and their Poisson variances are modified with the aid of chi(2) values of repeatedly measured intensities. Refinement on \F\(2) including weak and negative intensities. Anharmonic motion of N and O up the third order of a Gram-Charlier expansion was refined. R = 0.032, wR = 0.026, S-2 = 1.99, 3642 measured and 317 unique intensities, 17 parameters. Synchrotron X-ray diffraction: lambda = 0.56 Angstrom, F(000) = 78e, refinement on \F\. Anharmonic motion of N and O up to the fourth order of a Gram-Charlier expansion was refined. R = 0.020, wR = 0.007, S-2 = 1.51, 443 unique intensities, 39 parameters. No +/- 180 degrees Ising-type in plane orientational disorder of NO3-groups is observed at 293 K. Multipolar expansion of the electron density reveals bonding electrons and a strong deformation of the atoms within the planar NO3-group.