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

Abstract

Guided ion beam tandem mass spectrometry was used to examine the kinetic energy dependent reactions of U+ with O2 and CO. In the reaction of U+ with O2, the UO+ product is formed in a barrierless and exothermic process with a reaction efficiency at low energies of k/kcol=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 D0(U+‐O)=7.88±0.09 eV and D0(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 D0(U‐O)=7.82 eV and D0(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).

f-Block reactions of metal cations with carbon dioxide studied by inductively coupled plasma tandem mass spectrometry

“…11 The Th + and U + efficiencies reported here compare well with the ion beam 11,22 and FTICR-MS results from Cornehl et al 38 The FTICR-MS measurements of Gibson and coworkers 1,2 are lower than those observed here with the exception of Pu + and Am + where very inefficient reactions under nominally thermal conditions were observed in the FTICR-MS work. Note that the FTICR-MS measurements of Gibson and coworkers 1,5 are systematically lower than those observed in GIBMS experiments as observed for several reactions with Th + , 13,18,22,40 U + , 23 and Gd + . 14,16 The differences in k / k col between measurements has been previously attributed to a different starting ion electronic energy distribution.…”

“…4 is semiquantitative estimating intermediate well depths from Sm + CID reactions 15 and product energies from UO + and PuO + BDEs. 23,39…”

“…GIBMS 10–27 oxidation studies shed light on the reaction by observing it over a wide range of kinetic energies. The energy dependence of the reaction often simplifies the interpretation of results, as noted in the GIBMS study of Th + + CH 4 , 10 and allows the observation of endothermic reactions or reactions with a barrier.…”

Coupled Cluster Study of the Heats of Formation of UF6 and the Uranium Oxyhalides, UO2X2 (X = F, Cl, Br, I, and At)

“…The final values agreed within the experimental uncertainties in the 3 cases in which experimental values were available, but unfortunately these uncertainties ranged from 2.4 to 5.5 kcal/mol. Based on previous investigations, − ,, the FPD atomization enthalpies are expected to be accurate to within 3 kcal/mol. Enthalpies of formation were calculated for each species by making use of available experimental heats of formation with FPD atomization enthalpies as well as two different FPD-calculated reaction enthalpies involving UF 6 , UO 2 X 2 , H 2 O, and HX species.…”

“…Over the past few years, we have been modifying the Feller–Peterson–Dixon (FPD) composite approach , to address the accurate calculation of the thermochemical properties of actinide-containing molecules. By accounting for correlation effects via the coupled cluster method, inclusion of outer-core correlation, scalar relativity from the outset, and spin–orbit coupling using 2-component or 4-component correlated methods, bond dissociation enthalpies have been obtained that in some instances have rivaled the best experimental values, primarily for Th-containing molecules − but also recently including small uranium-containing species. − …”