Title: Computed vibrational frequencies of actinide oxides AnO0/+/2+ and AnO20/+/2+ (An = Th, Pa, U, Np, Pu, Am, Cm)
Citation: JOURNAL OF PHYSICAL CHEMISTRY A vol. 115 no. 24 p. 6646 – 6656
Publication Year: 2011
JRC N°: JRC64469
ISSN: 1089-5639
URI: http://pubs.acs.org/doi/abs/10.1021/jp202538k
DOI: 10.1021/jp202538k
Type: Articles in periodicals and books
Abstract: The vibrational frequencies of the actinide oxides AnO and AnO2 (An = Th, Pa, U, Np, Pu, Am, Cm) and of their mono- and dications have been calculated using advanced quantum chemical techniques. The stretching fundamental frequencies of the monoxides have been determined by fitting the potential function to single-point energies obtained by relativstic CASPT2 calculations along the stretching coordinate and on this basis solving numerically the ro-vibrational Schrödinger equitation. To obtain reliable fundamental frequencies of the dioxides, we developed an empirical approach. In this approach the harmonic vibrational frequencies of the AnO20/+/2+ species were calculated using eight different exchange-correlations DFT functional. On the basis of the good correlation found between the vibrational frequencies and computed bond distances, the final frequency values were derived for the CASPT2 reference bond distances from linear regression equitations fitted to the DFT data of each species, As test, the approach provided excellent agreement with accurate experimental data of ThO, ThO+, UO and UO+. The joint analysis of literature experimental and our computed data facilitated the prediction of reliable gas-phase molecular properties for some oxides. They include the stretching frequencies of PuO, ThO2, Uo2 and Uo2+ and the bond distance of PuO (1.818 Å. being likely within 0.002 Å of the real value). Also the derived equilibrium bond distances of ThO2, UO2 and UO2+ (1.896, 1.790 and 1.758 Å, respectively) should approximate closely the (yet unknown) experimental values. On the basis of the present results we suggest that the ground electronic state of PuO2 in Ar and Kr matrices is probably different from that in the gaseous phase, similarly to UO2 observed previously.
JRC Directorate:Nuclear Safety and Security

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