Uranium Oxo and Superoxo Cations Revealed Using Infrared Spectroscopy in the Gas Phase
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Abstract
The UO<sub>4</sub><sup>+</sup> and UO<sub>6</sub><sup>+</sup> cations are produced in a supersonic molecular beam by laser vaporization and studied with infrared laser photodissociation spectroscopy using rare gas atom predissociation. The argon complexes UO<sub>4</sub><sup>+</sup>Ar<sub>2</sub> and UO<sub>6</sub><sup>+</sup>Ar<sub>2</sub> are mass-selected in a reflectron time-of-flight spectrometer and excited with an IR-OPO laser system in the range of the O–U–O and O–O stretching vibrations. These same systems are studied with computational quantum chemistry. UO<sub>4</sub><sup>+</sup> is found to have a central UO<sub>2</sub> core, with an additional η<sup>2</sup> coordinated oxygen molecule. Charge transfer/oxidation gives the system the character of a UO<sub>2</sub><sup>2+</sup>, O<sub>2</sub><sup>–</sup> ion pair. UO<sub>6</sub><sup>+</sup> has this same core structure, with an additional weakly bound oxygen molecule in an η<sup>1</sup> coordination configuration. The O–U–O stretch is sensitive to the local environment and approximates the vibration of the isolated uranyl cation in these systems