Modeling IR spectra of uranium monoxide clusters

Structural models were designed and spectral characteristics were computed based on DFT calculations of uranium monoxide clusters (UO)2, (UO)4, (UO)6, and (UO)9. Spectral features that were characteristic of the cluster formation process were identified. The uranium oxidation state was close to 3 in the clusters (UO)2, (UO)4, and (UO)6. The vibrational frequencies decreased monotonically in the sequence (UO)2 → (UO)4 → (UO)6 because of decreasing electron density in each of the UO bonds with the growing complexity of the clusters. The uranium oxidation state was close to 4 in the cluster (UO)9. This led to a strengthening of the bonds and an increase in the frequency of the strongest band in the IR spectrum. (author)