ANHARMONIC MOTION AND MULTIPOLAR EXPANSION OF THE ELECTRON-DENSITY INNANO3

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 chec ked for normal and independent distribution and their Poisson variance s are modified with the aid of chi(2) values of repeatedly measured in tensities. Refinement on \F\(2) including weak and negative intensitie s. 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 measure d and 317 unique intensities, 17 parameters. Synchrotron X-ray diffrac tion: lambda = 0.56 Angstrom, F(000) = 78e, refinement on \F\. Anharmo nic motion of N and O up to the fourth order of a Gram-Charlier expans ion was refined. R = 0.020, wR = 0.007, S-2 = 1.51, 443 unique intensi ties, 39 parameters. No +/- 180 degrees Ising-type in plane orientatio nal disorder of NO3-groups is observed at 293 K. Multipolar expansion of the electron density reveals bonding electrons and a strong deforma tion of the atoms within the planar NO3-group.