Engineering topics

Ciborowski, Sandra M.

Publications and source records attributed to Ciborowski, Sandra M..

3 records

DOE OSTI2022

Experimental and Computational Description of the Interaction of H and H – with U

In this work, the results of ab initio correlated molecular orbital theory electronic structure calculations for low-lying electronic states are presented for UH and UH – and compared to photoelectron spectroscopy measurements. The calculations were performed at the CCSD(T)/CBS and multireference CASPT2 including spin–orbit effects by the state interacting approach levels. The ground states of UH and UH – are predicted to be 4 Ι 9/2 and 5 Λ 6 , respectively. The spectroscopic parameters T e , r e , ω e , ω e x e , and Be were obtained, and potential energy curves were calculated for the low energy Ω states of UH. The calculated adiabatic electron affinity is 0.468 eV in excellent agreement with an experimental value of 0.462 ± 0.013 eV. The lowest vertical detachment energy was predicted to be 0.506 eV for the ground state, and the adiabatic ionization energy (IE) is predicted to be 6.116 eV. The bond dissociation energy (BDE) and heat of formation values of UH were obtained using the IE calculated at the Feller–Peterson–Dixon level. For UH, UH – , and UH + , the BDEs were predicted to be 225.5, 197.9, and 235.5 kJ/mol, respectively. The BDE for UH is predicted to be ~20% lower in energy than that for ThH. The analysis of the natural bond orbitals shows a significant U + H – ionic component in the bond of UH.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Metal–Metal Bonding in Actinide Dimers: U 2 and U 2 –

Understanding direct metal–metal bonding between actinide atoms has been an elusive goal in chemistry for years. Here we report for the first time the anion photoelectron spectrum of U 2 – . The threshold of the lowest electron binding energy (EBE) spectral band occurs at 1.0 eV, which corresponds to the electron affinity (EA) of U 2 , whereas the vertical detachment energy of U 2 – is found at EBE ~ 1.2 eV. Electronic structure calculations on U 2 and U 2 – were carried out with state-of-the-art theoretical methods. The computed values of EA(U 2 ) and EA(U) and the difference between the computed dissociation energies of U 2 and U 2 – are found to be internally consistent and consistent with experiment. Analysis of the bonds in U 2 and U 2 – shows that while U 2 has a formal quintuple bond, U 2 – has a quadruple bond, even if the effective bond orders differ only by 0.5 unit instead of one unit. Furthermore, the resulting experimental-computational synergy elucidates the nature of metal–metal bonding in U 2 and U 2 – .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

The electron affinity of the uranium atom

The results of a combined experimental and computational study of the uranium atom are presented with the aim of determining its electron affinity. Experimentally, the electron affinity of uranium was measured via negative ion photoelectron spectroscopy of the uranium atomic anion, U – . Computationally, the electron affinities of both thorium and uranium were calculated by conducting relativistic coupled-cluster and multi-reference configuration interaction calculations. The experimentally determined value of the electron affinity of the uranium atom was determined to be 0.309 ± 0.025 eV. The computationally predicted electron affinity of uranium based on composite coupled cluster calculations and full four-component spin–orbit coupling was found to be 0.232 eV. Predominately due to a better convergence of the coupled cluster sequence for Th and Th – , the final calculated electron affinity of Th, 0.565 eV, was in much better agreement with the accurate experimental value of 0.608 eV. In both scenarios, the ground state of the anion corresponds to electron attachment to the 6d orbital.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗