Photodissociation and Theory to Investigate Uranium Oxide Cluster Cations.

Uranium oxide cluster cations of the form UO are produced by laser vaporization of a depleted uranium rod in a pulsed supersonic expansion. Ions are mass-analyzed and mass-selected with a time-of-flight spectrometer and studied with UV laser multiphoton dissociation. Cations of the stoichiometry UO(UO) were observed as photofragments from all photodissociated cluster cations. (UO) clusters were also observed to result from dissociation of larger (UO) clusters, with UO neutral as a common leaving group. Electronic structure calculations were used to investigate the stability of the prominent uranium oxide cluster cations using density functional theory (DFT) with the hybrid B3LYP exchange-correlation functional and at the CCSD(T) level with cc-pVnZ-PP basis sets (n = D,T), including diffuse orbitals as computational expense and availability permitted. Clustering energies, relative energies and dissociation energies of the cations are reported. The lowest energy neutral (UO) clusters up to = 3 are rings, = 4 and 5 are chains with very low energy rings, and = 6 is 3D. The lowest energy structures for UO(UO) are composed of uranyl-like UO units bound by bridging oxygens to other UO units for = 2 and 3, and for = 4 a more complex 3D structure is predicted.