LASER SPECTROSCOPY OF UO - CHARACTERIZATION AND ASSIGNMENT OF STATES IN THE 0-EV TO 3-EV RANGE, WITH A COMPARISON TO THE ELECTRONIC-STRUCTURE OF THO

Wavelength-resolved fluorescence excitation techniques have been used to record 33 electronic transitions of UO at a resolution of 0.03 cm-1 . Nine low-lying electronic states that correlated with either U2+(5f( 3)7s)O2- or U2+(5f(2)7S2)O2- were characterized. With few exceptions, OMEGA assignments were unambiguously determined from observations of t he first lines in at least two rotational branches. Accurate term ener gies and rotational constants are reported. Deperturbed constants of o mega(e) = 846.5 cm-1 and R(e) = 1.8383 angstrom have been determined f or the ground state of the 5f(3)7s configuration, and omega(e) = 934.9 cm-1 and R(e) = 1.7932 angstrom for states of the 5f(2)7s' configurat ion. Ligand field theory models were used to analyze the low-energy el ectronic structure of UO. Fitted values of the ligand field parameters B0(2)(5f) = 6488, B0(4)(5f) = 742, and B0(6)(5f) = 118 cm-1 did not a gree with values calculated using a relativistic Dirac-Fock formalism B0(2)(5f) = 26 130, B0(4)(5f) = 12 130, and B0(6)(5f) = 12 020 cm-1). Ligand field theory calculations were also used in an attempt to provi de configurational assignments for the excited states of UO and ThO. E xperimentally derived values for DELTAB0(0)(nl/n'l') parameters were u sed to predict the electronic structures of UO and UO'. The energies o f 23 electronic configurations of UO, and 19 electronic configurations of UO+, have been calculated. The density distributions of the bound states of UO and UO+ up to their ionization limits were also calculate d. (C) 1994 Academic Press. Inc.