The structural and spectroscopic properties for uranium oxides

The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO_2, UO_3, and U_2O_3 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, UO_2 , and UO_3 molecules are all in agreement with available experimental data. For U_2O_3 molecules, our calculations indicate that the ground state of the U_2O_3 molecule is an \tilde \rm X^7A_1^\prime state with D_3h (trigonal bipyramid) symmetry (R_1(U--O)=0.2113 nm, R_2(U_1--U_2)=0.2921 nm, \angleU_1OU_2=87.5^\circ , dihedral angle \varTheta (U,O_1,O_2,O_3)=62.40^\circ). The harmonic frequency, the IR intensity and the spin density of the U_2O_3 molecule are all obtained for the first time in theory. For the ground state of U_2O_3 molecules, the vibrational frequencies are 178.46 (A_1^\prime), 276.79 (E_1''), 310.77 (E_1^\prime), 396.63 (A_2''), 579.15 (E_1^\prime), and 614.98 (A_1^\prime) cm^ - 1. The vibrational modes corresponding to the IR maximum peaks are worked out for UO_3 and U_2O_3 molecules. Besides, the results of Gophinatan--Jug bond order indicate that UO, UO_2 , and UO_3 molecules possess U=O double bonds and that the U_2O_3 molecule possesses U--O single bonds and a U--U single bond.