Theoretical study on the reaction between uranium and O-2

Investigating the electronic structure of the products of uranium oxidation and the electron transfer in this process, and revealing the mechanism on the initial oxidation stage of uranium surface are of great importance for finding out the effective anti-corrosion methods of uranium surface. In thi s paper, optimized geometries, total energies and electronic structures of some gaseous atoms and molecules of uranium-oxygen system are calculated wi th harmonic vibration analyses using ab initio method. Some potential energ y surfaces (PESs) of the uranium oxidation process are also constructed. Th e calculated geometric parameters and infrared vibrational frequencies of s ome uranium oxides are consistent very well with experimental data. The PES s show that different reaction modes result in different product geometries . When U approaches O-2 at the oxygen atom top along the axis of O-O bond, a relatively stable linear structure, O-O-U, is formed, which has: the poss ibility to decompose to UO and O. When U approaches O-2 along the perpendic ular median of the O-O bond axis, a stable molecule UO2 comes into being vi a two bent metastable structures with bond angles of about 151 and 105 degr ees, respectively. No potential energy barrier is needed for the uranium an d O-2 to form the metastable states, while a very little barrier is needed to form the stable linear UO2 from the metastable structures. And for the r eaction O + UO --> OUO (linear) also, there is no potential energy barrier needed, while for the reaction O + OU --> U . . .O . . .O (linear), a barri er of about 4.5 eV is needed. U5f atomic orbital electrons dominate in the formation of the U-O bonds. (C) 2001 Elsevier Science B.V. All rights reser ved.