X-ray spectroscopic study of chemical state in uranium carbides

UC and UMeC2 (Me = Fe, Zr, Mo) carbides were studied by the high-energyresolution fluorescence-detected X-ray absorption (HERFD-XAS) technique at the U M-4 and L-3 edges. Both U M-4 and L-3 HERFD-XAS reveal some differences between UMeC2 and UC; there are differences also between the M-4 and L-3 edge results for both types of carbide in terms of the spectral width and energy position. The observed differences are attributed to the consequences of the U 5f, 6d-4d(3d) hybridization in UMeC2. Calculations of the U M-4 HERFD-XAS spectra were also performed using the Anderson impurity model (AIM). Based on the analysis of the data, the 5f occupancy in the ground state of UC was estimated to be 3.05 electrons. This finding is also supported by the analysis of U N-4,N-5 XAS of UC and by the results of the AIM calculations of the U 4f X-ray photoelectron spectrum of UC.