The Th M/sub 3/O/sub 1/ (/sup 3/p/sub 3/2/sup -1/..-->..5s/sup -1/) x-ray emission spectrum of ThO/sub 2/ was measured with a high-resolution vacuum double-crystal spectrometer. The spectrum shows the first evidence of the splitting of a 5s hole level into two main structures which are due to a strong configuration interaction: 5s/sup -1/left-right-arrow5p/sup -1/5d/sup -1/5(n,epsilon)f super-Coster-Kronig process. The O/sub 1//sub a/ and O/sub 1//sub b/ hole energies of ThO/sub 2/ determined by the present measurements are, respectively, 293.9 and 276.2 eV. A large energy shift (order of approx. =15 eV) to lower binding energy from the theoretically predicted atomic energies is observed even when one takes into account the atom-oxide energy shift. The cause of discrepancy is suggested to be due to a strong configuration interaction of the final 5p5d double hole: 5p/sup -1/5d/sup -1/left-right-arrow5d/sup -3/5(n,epsilon)f.
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