The synthesis and characterization of the ternary U-O-N compound NO+UO2(NO3)(3)(-) (1) using IR and low-temperature and room-temperature Raman spectroscopy as well as N-14 and N-15 NMR spectroscopy are reported. In addition, solution Raman spectra of compound 1 recorded in various solvents are reported. The structure of compound 1 was determined using single-crystal X-ray diffraction techniques: monoclinic, C21c, a = 13.3992(4) angstrom, b = 9.9781(4) angstrom, c = 7.6455(2) angstrom,beta = 115.452(2)degrees, V = 922.98(5) angstrom(3), Z = 4. Compound 1 is highly moisture-sensitive and must be handled under an inert atmosphere. It reacts with water with the liberation of NO2. For the first time, this important precursor for the synthesis of anhydrous uranyl nitrate could be unambiguously identified and has been shown to be an ionic nitrosonium salt and not an adduct between uranyl nitrate and dinitrogen tetroxide, UO2(NO3)(2)center dot-N2O4, as is incorrectly and predominantly cited in the literature.