The electronic structure of thorium monoxide: Ligand field assignment of states in the range 0–5 eV

Abstract

Configuration interaction ligand field theory (CI LFT) calculations of the electronic energy levels of ThO were performed by treating the molecular electronic states as Th 2+ free-ion levels perturbed by the ligand field of O 2− . Twenty nine experimentally characterized ThO v = 0 energy levels, together with the energy difference between the v = 0 levels of the Y and W states were fitted using a CI LFT model that included Th 2+ 7s 2 , 6d7s, 6d 2 , 7s7p, 6d7p, 5f7s, and 7p 2 configurations. Predictions from these calculations were used to provide tentative assignments for 171 out of 250 ThO band heads listed by Gatterer et al.["Molecular Spectra of Metallic Oxides", Specola Vaticana (1957)]. Term energies for 30 electronic states have been determined based on these assignments. Subsequently, the CI LFT model was refined by fitting to a set of 59 electronic term energies. The inclusion of CI effects together with integer valence, atomic-in-molecule, ionic bonding ideas reveals atomic energy level patterns that are multiply replicated in the molecular energy level patterns of six Th 2+ O 2− atomic ion configurations (6d7s, 6d 2 , 7s7p, 6d7p, 5f7s, and 7p 2 ) revealing the underlying atomic ion structure that gives rise to the complex and seemingly erratic unassigned bands reported in the Vatican Atlas.

The metastable Q 3Δ2 state of ThO: a new resource for the ACME electron EDM search

“…The values of g Q extracted from the two fitted linear slopes, Δ σ and Δ π , are 2.08(2) and 2.06(3), respectively, where the values in parentheses are statistical uncertainties. We assign a final value as the weighted mean of the results, yielding g Q =2.07 (11). The uncertainty is dominated by systematic contributions from our estimates of the -field calibration (5%) due to uncertainty in the Helmholtz coil geometry, and the frequency calibration error (1%) of the scanning FP cavity.…”

“…Branching ratios to intermediate states other than X, Q, and H, i.e. A, B, ¢ H , ¢ K , and ¢ N , are estimated based on the amplitudes of their decomposition in the Hund's case (a) basis [11] and the wavelengths for decay to them from ¢ = C v 0 (…”

The electronic structure of the actinide oxides and their singly and doubly charged cations: A ligand field approach

“…The ( α n l / α ′n′ l ′) values were recently determined from configuration interaction ligand field theory (CI LFT) calculations of the electronic energy levels of ThO [12]. It should be noted that, for two‐electron configurations of ThO with two equivalent 6 d or 7 s electrons in the 6 d 2 or 7 s 2 shells, two separate sets of ( α n l / α ′n′ l ′) were used in addition to the set of ( α n l / α ′n′ l ′) for non‐equivalent electrons in the n l n′ l ′ shells [13, 14].…”

“…It should be noted that, for two‐electron configurations of ThO with two equivalent 6 d or 7 s electrons in the 6 d 2 or 7 s 2 shells, two separate sets of ( α n l / α ′n′ l ′) were used in addition to the set of ( α n l / α ′n′ l ′) for non‐equivalent electrons in the n l n′ l ′ shells [13, 14]. The ( α n l / α ′n′ l ′) values are also available from previous LFT analyses of ThO [12, 15], UO [15], ThO + [16], and UO + [17] electronic spectra. They are presented in Tables S1 and S2.…”

“…As a consequence, the ratios of calculated and experimentally determined ( α n l , α n l ) values should be approximately constant across the actinide series. Assuming that the ratios are invariant across the actinide series, values of LFT fitted parameters can be used for the calculation of throughout the entire An 4+ O 2− , An 3+ O 2− , An 2+ O − , An 2+ O 2− and An + O − series using ratios of calculated LFT parameters and fitted ( α n l , α n l ) parameters for ThO [12, 15], UO [15], ThO + [16] and UO + [17] according to the scaling relationship: where An O∈ThO, UO and An O + ∈ThO + , UO + (see Table S4 where the fitted values are in bold). In view of the approximate character of the calculations, it was preferable to use a fixed value for the internuclear distance of R e = 1.8 Å throughout the entire An 4+ , An 3+ , An 2+ , and An + series, rather than trying to extrapolate R e for each individual configuration using the available data for Th and U monoxides and their ions.…”