Reaction of laser-ablated uranium atoms with CO: Infrared spectra of the CUO, CUO-, OUCCO, (eta(2)-C-2)UO2,-and U(CO)(x) (x=1-6) molecules in solid neon

Laser-ablated uranium atoms have been reacted with CO molecules during cond ensation with neon at 4 K. Absorptions at 1047.3 and 872.2 cm(-1) are assig ned to the CUO molecule formed from the insertion reaction that requires ac tivation 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 ultraviolet-visible photo n-induced rearrangment of the U(CO)(2) molecule. The OUCCO molecule undergo es further photochemical rearrangment to the (C-2)UO2 molecule, which is ch aracterized 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- anio n and U(CO)(x)(-) (x = 1-5) anions, which are formed by electron capture. R elativistic density functional theoretical calculations have been performed for the aforementioned species, which lend strong support to the experimen tal assignments of the infrared spectra. It is predicted that CUO is a line ar singlet molecule with the shortest U-C bond yet characterized, and it ha s a U-C triple bond with substantial U 5f character. The theoretical analys is also finds that a distorted tetrahedral geometry of (C-2)UO2 lies much l ower in energy than either the bent/linear OUCCO structures or the U(CO)(2) uranium dicarbonyl.