Decay channels of the5d→5fexcitation in thorium

The valence bands and Auger emission of thorium have been studied in the 5d→5f excitation region using synchrotron radiation. Three decay channels of the 5d hole have been identified: ordinary Auger deexcitation, resonant Auger deexcitation, and direct recombination. The latter two originating from strongly exchange-coupled 5$d^9$5$f^1$ virtually excited states. A kinetic energy shift of the $O_5$VV Auger line is observed around a 5d→5f resonant absorption peak at hν=89 eV and is attributed to overlap of the above two Auger features. The relative importance of these decay channels is discussed in terms of the discrete 5$d^9$5$f^1$→continuum 5$d^9$εf transition probability and the 5d→5f dipole oscillator strength of the 5$d^9$5$f^1$ multiplet state.