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

Spectroscopic and thermodynamics properties including bond dissociation energies (BDEs), adiabatic electron affinities (AEAs), and ionization energies (IEs) have been predicted for AcH and PaH using the Feller-Peterson- Dixon composite approach. Comparisons with previous studies on ThH and UH were performed to identify possible trends in the actinide series. Multireference CASPT2 calculations were used to predict the spin-orbit effects and obtain potential energy curves for the low-lying omega states around the equilibrium distance as well as the vertical detachment energies (VDEs) from AcH- and PaH- to excited states of the neutral species. The calculated AEA for AnH (An = Ac, Th, Pa, U) showed that the AEA increases from AcH (0.425 eV) to ThH (0.820 eV) and decreases to PaH (0.781 eV) and to UH (0.457 eV), whereas the IE values are 5.887 eV (AcH), 6.181 eV (ThH), 6.204 eV (PaH), and 6.182 eV (UH). The ground state of AcH, AcH-, PaH, and PaH- are predicted to be1 sigma+0,2 pi 3/2, 3H4, and 4I9/2, respectively. The BDEs for AcH and PaH are 276.4 and 237.2 kJ/mol, and those for AcH- and PaH(- )are 242.8 and 239.8 kJ/mol, respectively. The natural bond analysis shows a significant ionic character, An(+)H(-), in the bonding of the neutral hydrides.

Automated summary

In this study, spectroscopic and thermodynamic properties of AcH and PaH were predicted using the Feller-Peterson-Dixon composite approach. The results were compared with previous studies on ThH and UH to identify trends in the actinide series. It was found that there are differences in the adiabatic electron affinities, ionization energies, and bond dissociation energies among the different compounds.