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

Abstract

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 –(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 n 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 n 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.

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