Electronic Configuration Assignments for UO from Electric Dipole Moment Measurements

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+(5f37s)O2- and U2+(5f27s2)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 (mu e) of an electronic state should also manifest a value that is characteristic of the parent electronic configuration. mu 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 mu 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+(5f37s)O2- and U2+(5f27s2)O2- configurations, respectively.