Computationally Guided Investigation of the Optical Spectra of Pure β-UO3

Single-phase beta-UO3 is synthesized by flash heating UO2 (NO3)center dot 6H(2)O in air to 450 degrees C and annealing for 60 h under the same conditions. For the first time, we report the Raman spectra of pure beta-UO3. To facilitate the assignment of Raman and infrared vibrational modes, we use density functional theory with density functional perturbation theory. By employing a novel analysis scheme that includes the mode frequencies as well as a quantitative analysis of the mode eigenvectors, we assign the observed spectral features to individual chemical modes. In particular, the density functional theory optimized structure, observed Raman spectrum, and eigenvector analysis suggest the presence of four crystallographically distinct uranyl ions, one more than has previously been suggested.