Electronic Structure and Anion Photoelectron Spectroscopy of Uranium-Gold Clusters UAu^-, n = 3-7

A collaborative effort between experiment and theory toward elucidating the electronic and molecular structures of uranium-gold clusters is presented. Anion photoelectron spectra of UAu^-(n = 3-7) were taken at the third (355 nm) and fourth (266 nm) harmonics of a Nd:YAG laser, as well as excimer (ArF 193 nm) photon energies, where the experimental adiabatic electron affinities and vertical detachment energies values were measured. Complementary first-principles calculations were subsequently carried out to corroborate experimentally determined electron detachment energies and to determine the geometry and electronic structure for each cluster. Except for the ring-like neutral isomer of UAu₆ where one unpaired electron is spread over the Au atoms, all other neutral and anionic UAu clusters (n = 3-7) were calculated to possess open-shell electrons with the unpaired electrons localized on the central U atom. The smaller clusters closely resemble the analogous UF species, but significant deviations are seen starting with UAu₅ where a competition between U-Au and Au-Au bonding begins to become apparent. The UAu₆ system appears to mark a transition where Au-Au interactions begin to dominate, where both a ring-like and two heavily distorted octahedral structures around the central U atom are calculated to be nearly isoenergetic. With UAu₇, only ring-like structures are calculated. Overall, the calculated electron detachment energies are in good agreement with the experimental values.