PNNL

Abstract

Laser-ablated uranium atoms have been reacted with CO molecules during condensation with neon at 4 K. Absorptions at 1047.3 and 872.2 cm-1 are assigned to the CUO molecule formed from the insertion reaction that requires activation energy. Isotopic substitution shows that the upper band is largely U-C and the lower band mostly U-O in vibrational character. Absorptions at 2051.5, 1361.8, and 841.0 cm-1 are assigned to the OUCCO molecule, which is formed by the CO addition reaction to CUO and ultravioletvisible photon-induced rearrangment of the U(CO)2 molecule. The OUCCO molecule undergoes further photochemical rearrangment to the (C2)UO2 molecule, which is characterized by symmetric and antisymmetric OUO stretching vibrations at 843.2 and 922.1 cm-1. The uranium carbonyls U(CO)x (x ) 1-6) are produced on deposition or on annealing. Evidence is also presented for the CUO- anion and U(CO)x- (x ) 1-5) anions, which are formed by electron capture. Relativistic density functional theoretical calculations have been performed for the aforementioned species, which lend strong support to the experimental assignments of the infrared spectra. It is predicted that CUO is a linear singlet molecule with the shortest U-C bond yet characterized, and it has a U-C triple bond with substantial U 5f character. The theoretical analysis also finds that a distorted tetrahedral geometry of (C2)UO2 lies much lower in energy than either the bent/linear OUCCO structures or the U(CO)2 uranium dicarbonyl.