Bond Energies of UO+ and UC+: Guided Ion Beam and Quantum Chemical Studies of the Reactions of Uranium Cation with O2 and CO

Guided ion beam tandem mass spectrometry was used to examine the kinetic energy dependent reactions of U+ with O-2 and CO. In the reaction of U+ with O-2, the UO+ product is formed in a barrierless and exothermic process with a reaction efficiency at low energies of k/k(col)=1.1 +/- 0.2, but increases at higher collision energies. Formation of both UO+ and UC+ in the reaction of U+ with CO is endothermic. 0 K bond dissociation energies (BDEs) of D-0(U+-O)=7.88 +/- 0.09 eV and D-0(U+-C)=4.03 +/- 0.13 eV were determined by analyzing the kinetic energy dependent cross sections in the latter endothermic reactions. These values are within experimental uncertainty of previously reported experimental values. Additionally, the electronic states of UO+ and UC+ and the potential energy surfaces for the reactions were explored by quantum chemical calculations. The former include a full Feller-Peterson-Dixon composite approach with correlation contributions up to CCSDT(Q) for UO and UO+, yielding D-0(U-O)=7.82 eV and D-0(U+-O)=7.99 eV, as well as more approximate CCSD(T) calculations where a semi-empirical model was used to estimate spin-orbit energy contributions, which are generally found to improve the agreement with experiment. Both experimental BDEs are observed to be close to those of their transition metal congeners, ScL+, YL+, and GdL+ (L=O and C).

Automated summary

Guided ion beam tandem mass spectrometry was used to study the reactions of U+ with O-2 and CO. The formation of UO+ in the U+ + O-2 reaction is barrierless and exothermic, with a reaction efficiency that increases with higher collision energies. Both the formation of UO+ and UC+ in the U+ + CO reaction are endothermic. Analysis of the kinetic energy dependent cross sections reveals 0 K bond dissociation energies of D-0(U+-O)=7.88 +/- 0.09 eV and D-0(U+-C)=4.03 +/- 0.13 eV, which are consistent with previous experimental values. Quantum chemical calculations were also performed to explore the electronic states of UO+ and UC+ and the potential energy surfaces for the reactions, yielding further insights into the reaction mechanisms. The experimental bond dissociation energies are found to be similar to those of transition metal congeners.