Electronic Configuration Assignments for UO from Electric Dipole Moment Measurements

Abstract

Diatomic UO has more than 48 bound states within 10000 cm–1 of the ground state. This electronic state congestion has been attributed to interleaved states from the electronic configurations U2+(5f 37s)­O2– and U2+(5f 27s 2)­O2–, respectively. Ligand field theory predicts that each electronic configuration will exhibit states with distinguishable, characteristic vibrational and rotational constants. However, vibronic state mixing modifies the observed vibration–rotation constants, leading to uncertainty in the configurational assignments. The permanent electric dipole moment (μ e ) of an electronic state should also manifest a value that is characteristic of the parent electronic configuration. μ e and other electrostatic and magnetostatic properties should be less influenced by the vibronic state mixing, providing more robust indicators for configurational assignments. In the present study, we have measured the μ e values for four electronic states of UO. The results clearly demonstrate that the ground state (X(1)­4) and the first electronically excited state ((2)­4) are derived from the U2+(5f 37s)­O2– and U2+(5f 27s 2)­O2– configurations, respectively.

Energetic and Electronic Properties of UO0/± and UF0/±

“…For UO, the ground state is predicted to be Ω = 4 with a 7s 1 5f 3 configuration on U. Both the bond distance and frequency are consistent with prior work ,, and current calculations at the CCSD­(T)/aQ-DK level without SO (Table ). For UF, the ground state is predicted to be Ω = 4.5 (7s 2 5f 3 on U) and the SO-CASPT2/aQ-PP level spectroscopic parameters are consistent with those at the CCSD­(T)/aQ-DK and with prior work. , …”

“…Experimental data on the uranium oxides includes resonant enhanced multiphoton ionization (REMPI) studies, especially on UO, UO + , and uranium dioxide molecules (Table ). − The adiabatic ionization energy (IE) of UO is 6.0313 eV, with a ground state bond distance R e = 1.8383 Å and vibrational constants ω e = 846.5 cm –1 and ω e x e = 2.3 cm –1 . , Kaledin et al used coupled cluster singles and doubles with a perturbative estimate for connected triples [CCSD­(T)] theory to predict IE = 5.98 eV and the bond dissociation energy D e = 789.5 kJ/mol . A weighted average of six reported enthalpies of formation for UO gave Δ H f ° (298.15 K) = 21.4 ± 10 kJ/mol and D 0 = 758.9 ± 10 kJ/mol .…”