Matrix infrared spectra of the products of uranium-atom reactions with carbon monoxide and carbon dioxide

Uranium atoms from pulsed Nd:YAG laser ablation of a uranium metal target were codeposited with carbon monoxide and carbon dioxide in excess argon at 10 K. Infrared spectra following the U + CO reaction revealed strong new absorption bands at 804.4 and 852.6 cm^-1, which are assigned to the CUO product on the basis of isotopic shifts, FG matrix calculations, and ab initio pseudopotential calculations. An absorption at 2027.5 cm^-1 is attributed to the asymmetric secondary reaction product CU(O)CO. In both the U + CO and U + CO₂ reactions, bands at 870.9 and 1963.8 cm^-1 were observed and assigned to the association product of UO₂ and CO. Lastly, in the U + CO₂ experiments, new absorption band pairs were observed at 804.4 and 1799.6 cm^-1 and at 801.5 and 2011.7 cm^-1. The former pair was almost destroyed on annealing and is assigned to the OUCO insertion product. The latter pair is attributed to an OCU(O)CO species. The direct reaction of U atoms with CO and CO₂ requires an activation energy, which is provided by hyperthermal U atoms from pulsed laser evaporation.