Ionization Energies for the Actinide Mono- and Dioxides Series, from Th to Cm: Theory versus Experiment

Abstract

The results of a computational study with multiconfigurational quantum chemical methods on actinide monoxides (AnO) and dioxides (AnO(2)) for An = Th, Pa, U, Np, Pu, Am, and Cm, are presented. First and second ionization energies were determined and compared with experimental values, when available. The trend along the series is analyzed in terms of the electronic configurations of the various species. The agreement with experiment is excellent in most cases. Of particular interest is the first ionization of PuO(2). We applied cutting-edge theoretical methods to refine the ionization energy, but our computed data fall in the range of approximately 6 eV and not in the approximately 7 eV region as the experiment dictates. Such a system requires further computational and experimental attention.

Remarkably High Stability of Late Actinide Dioxide Cations: Extending Chemistry to Pentavalent Berkelium and Californium

“…These are followed energetically by the 3p u *a nd then by the 4s u *, both of whichcontain some contribution from the Oe lectrons. Electronic structureC ASSCF/CASPT2 calculations [23] have been reported for PaO 2 + to CmO 2 + and the results are in agreement with our values in Ta ble 3. The felectrons want to remain high spin so the 1d u and the 1f u take the first 4f electrons.A t Cm, the 3p u *b ecomes occupied and as econd f electron is added to the 3p u *f or Bk.…”

“…For No and Lr, the fe lectrons are added to the 3p u *. We note that filling the 3p u *l eads to ac hange in the oxidation state and No and Lr are no longer in the Vo xidation state for the AnO 2 + .N otably "actinyl" NoO 2 + is linear whereas LrO 2 + is bentt o1 078 with the linear structure4 .5 kcal mol À1 higher in energy.T he prior work [23] on linear AnO 2 + up to An = Cm showedt hat the these ions are dominated by a single configuration with at least the wavefunction being dominated by > 80 %o fasingle configuration. In fact, all of the AnO 2 0/ + /2 + were shown to be dominated by as ingle configurationi nt he CASPT2 calculations for Pa to Cm.…”

“…[53,[61][62][63] Only the geometries were optimized at the CCSD(T) level. The CCSD(T) method with the chosen basis set combination was chosen as acompromise between reliable predictions and computational efficiency.A sn oted above, the available multi-reference calculations [23] show that the electronic state of the AnO 2 + is dominated by as ingle reference so the CCSD(T) method is an acceptable computational approach. Because of the change in electron configurations between the "linear" and highly bent structures, av ery large multi-reference calculation would be required including the actinide 5f electrons and the O2 pe lectrons in an orbital space including the An 5f and 6d and O2 po rbitals.…”

Theoretical study of the electronic spectra of neutral and cationic NpO and NpO2

“…41 The goal of the present study is the systematic evaluation of the gas-phase electronic spectra of the neutral and ionic NpO and NpO 2 species by means of multireference relativistic ab initio calculations on the basis of our previous studies on the electronic ground states of these species. 12,38 Other important results from the present calculations are the energies of the excited states, required for a reliable evaluation of the thermodynamic functions of the gaseous oxides. Such thermodynamic data are utilized in developing safety procedures in nuclear industry.…”

“…10,11 Structural and vibrational data on the NpO and NpO 2 molecules are available from quantum chemical calculations only. 12,13 Experimental studies of the electronic structure were performed for the ions NpO 2 + and NpO 2 2+ and only in condensed phases. Early absorption spectra of Np oxides (and also other actinide compounds) were reviewed in Ref.…”