Quantitative conversion spectroscopy of the ultrasoft isomeric transition of uranium-235 and the electronic structure of uranium oxides

Combined measurements of conversion electron spectra and the decay constant (76.5 eV, (1/2)⁺→(7/2)⁻) of the E3-isomeric transition of the uranium-235 nucleus have been performed with collection of the isomer atoms on an indium surface. The conversion spectra are interpreted as corresponding to a mixture of two different oxides A and B of uranium, one of which (A) is similar to UO₂, and the other (B) consists of a uranium-oxygen cluster based on the linear uranyl group O-U-O. From a set of mixed experimental spectra conversion spectra have been found corresponding to the chemical states A and B of the isomer atoms, and the variation of the absolute intensities of the conversion lines has been quantitatively investigated for them by varying the chemical composition of the isomer atoms and the ratio between the intensities of various conversion lines of the B spectrum. Experimental ratios between the intensities of the conversion lines are compared with the expected ratios in accordance with the distribution of the 6p electron density in the uranyl group. It is concluded that the experimental data agree with the calculation and that abrupt violations of proportionality of the partial probabilities of conversion of the electron density near the nucleus are absent. In accordance with the hypothesis of proportionality of the partial probabilities of conversion, an experimental estimate is given of the degree of localization of the deep-lying uranium 6p _1/2 shell during formation of the chemical bond in the uranyl group: around 70% of the 6p _1/2 electron density remains in the quasi-atomic uranium shell and around 30% is transferred to hybrid molecular orbitals. Zh. éksp. Teor. Fiz. 112, 574–595 (August 1997)