L2andL3measurements of transition-metal5dorbital occupancy, spin-orbit effects, and chemical bonding

We present $L_2$ and $L_3$ x-ray absorption spectroscopy measurements on all of the $5d$ transition-metal ($T$) elements and selected $T{\mathrm{Al}}_2$ intermetallic compounds. For the $5d$ elements we discuss the general trends in the strength of the near-edge "white-line" (WL) feature, the manifestations of the spin-orbit effects, and the dearth of WL strength for Pt and Au. The changes in the intensity of the $L$-edge WL's in the intermetallic compounds $T{\mathrm{Al}}_2$ ($T=\mathrm{Au}\mathrm{and}\mathrm{Pt}$) are discussed in terms of strong $T$-Al chemical bonding. Interestingly, our results for this bonding in Au${\mathrm{Al}}_2$ are in good agreement with the arguments presented by Pauling [The Nature of the Chemical Bond (Cornell Univ. Press, Ithaca, NY, 1960), pp. 431-435].