In the field of actinide aqueous chemistry, this work aims to resolve some controversy about uranyl(VI) hydroxide species present in basic aqueous solutions. We revisit the Raman, IR, and UV-visible spectra with two new approaches. First, Raman, IR and UV data were recorded systematically from aqueous solutions with the noncomplexing electrolyte (C2H5)(4)NNO3 at 25 degrees C and 0.1 MPa ([U-total] = 0.005-0.105 M) in H2O and D2O over a wide range of -log mH(D)(+) between 2.92 and 14.50. Second, vibrational spectra (IR and Raman) of basic solutions in H2O and D2O were analyzed using the Bayesian Positive Source Separation method to estimate pure spectra of individual species. In D2O solutions, the new spectroscopic data showed the occurrence of the same species as those in H2O. As observed for the wavenumber of the symmetric stretching mode, the wavenumber characteristic of the O=U=O antisymmetric stretching mode decreases as the number of OH(D)(-) ligands increases. These kinds of data, completed by (1) analysis of the signal widths, (2) persistence of the apparent exclusion rule between IR and Raman spectra of the uranyl species stretching modes, and (3) interpretation of the absorption UV visible spectra, allow discussion of the chemistry, structures, and polynuclearity of uranyl(VI) species. In moderate basic solutions, the presence of two trimers is suggested. In highly basic solutions ([OH-] approximate to 3 M), the two monomers UO2(OH)(4)(2-) and UO2(OH)(5)(3+) are confirmed to be in good agreement with earlier EXAFS and NMR results. The occurrence of the UO2(OH)(6)(4-) monomer is also suggested from the more basic solutions investigated.