N-14 magic-angle spinning NMR spectra are obtained and analyzed for the nitrate ions of the two isomorphous room-temperature phases RbNO3(IV) and CsNO3(II). The analysis reveals that only a single set of N-14 quadrupole coupling (C-Q, n(Q)) and chemical shift anisotropy parameters, corresponding to one NO3- ion, is required for fitting the spectra. This contrasts the published XRD crystal structures, which show the presence of three non-equivalent NO3- ions in the unit cell. WIEN2k DFT calculations of the C-Q, n(Q) parameters combined with structure optimization (WIEN2k) lead to a refined crystal structure for CsNO3(ii) and excellent agreement with the experimental C-Q, n(Q) values. (C) 2004 Elsevier B.V. All rights reserved.