The structural and spectroscopic properties for uranium oxides

The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO₂, UO₃, and U₂O₃ molecules are systematically investigated using the density functional theory (DFT) with the method of generalized gradient approximation (GGA). The bond lengths and the vibrational frequencies of the ground states of UO, UO₂, and UO₃ molecules are all in agreement with available experimental data. For U₂O₃ molecules, our calculations indicate that the ground state of the U₂O₃ molecule is an X⁷A₁^′ state with D_3h (trigonal bipyramid) symmetry (R₁(U-O)=0.2113 nm, R₂(U₁-U₂)=0.2921 nm, angleU₁OU2=87.5°,dihedral angle θ(U,O₁,O₂,O₃)=62.40^°). The harmonic frequency, the IR intensity and the spin density of the U₂O₃ molecule are all obtained for the first time in theory. For the ground state of U₂O₃ molecules, the vibrational frequencies are 178.46 (A₁^′), 276.79 (E^″₁), 310.77 (E₁^′), 396.63 (A^″₂), 579.15 (E₁^′), and 614.98 (A₁^′) cm^-1. The vibrational modes corresponding to the IR maximum peaks are worked out for UO₃ and U₂O₃ molecules. Besides, the results of Gophinatan-Jug bond order indicate that UO, UO₂, and UO₃ molecules possess U=O double bonds and that the U₂O₃ molecule possesses U-O single bonds and a U-U single bond.