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

Abstract

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 B e 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.

Protactinium and Actinium Monohydrides: A Theoretical Study on Their Spectroscopic and Thermodynamic Properties

“…Calculations on the ionization energies were also obtained and displayed in Table . The EA of AcH (0.425 eV) is estimated to be the lowest value within the four first members of the actinide series and is similar to the one for UH (0.457 eV), which showed excellent agreement with the experiment . Note that most of the contribution for the AEA is due to the large SO correction of 0.254 eV obtained at the SO-CASPT2 level.…”

“…The calculations also show how the electron binding affects the order of the states now that the 5f orbitals are occupied. Previous work on ThH x /ThH x – ( x = 1 to 5) , and UH/UH – using the FPD method and multireference SO-CASPT2 to recover spin-orbit effects predicted an electron affinity of 0.820 eV for thorium monohydride and 0.468 eV for uranium monohydride as well as vertical detachment energies (VDEs) in good agreement with the experimental values from photoelectron experiments.…”

“…Bond dissociation energies (BDEs) were predicted for the AcH 0/+ and PaH + diatomics following the FPD approach (Table ). For comparison, the FPD components for the BDE of UH + are included . AcH and AcH + were dissociated to Ac + H and Ac + + H; PaH + was dissociated to Pa + + H, and UH + was dissociated to U + + H. As discussed in our prior study, high-level calculations of the U and Pa atom including spin-orbit effects are difficult to perform due to their 5f n 6d 1 7s 2 ( n = 2 or 3) configurations.…”

“…For comparison, the FPD components for the BDE of UH + are included . AcH and AcH + were dissociated to Ac + H and Ac + + H; PaH + was dissociated to Pa + + H, and UH + was dissociated to U + + H. As discussed in our prior study, high-level calculations of the U and Pa atom including spin-orbit effects are difficult to perform due to their 5f n 6d 1 7s 2 ( n = 2 or 3) configurations. Such calculations are feasible for the atomic cations as well as for the neutral AcH and ThH, which do not involve 5f electrons in the atomic ground states.…”

“…In the current work, following the methodologies developed in our prior studies, − we extended our calculations to PaH/PaH – and AcH/AcH – to predict their spectroscopic and thermodynamic properties. Thus, we can now examine the electronic structure and bond formation of the first four atoms of the actinide series when bonded to hydrogen.…”