Electronic structure of metal hydrides. III. Photoelectron spectroscopy studies of ScH2, YH2, and LuH2

Abstract

Photoelectron spectroscopy with synchrotron radiation has been used to examine the electronic energy bands of Sc${\mathrm{H}}_{1.85}$, Y${\mathrm{H}}_{1.73}$, and Lu${\mathrm{H}}_{1.77}$ for $15\le h\nu \le 100$ eV. The $h\nu$-dependent features in the bonding band are discussed in terms of initial-state densities of state and variations in the partial photoionization cross sections. The photoelectron spectroscopy results are combined with those of our earlier optical studies and are used to assess quantitatively the validity of the one-electron band model for $d$-band metal dihydrides. Good overall agreement is found when compared to the results of recent calculations, notably those of Peterman et al., based on the model proposed by Switendick. Band-structure effects are discussed in detail. Emission from the shallow $3p$, $4p$, and $5p$ core levels are revealed through high-photon-energy spectra. Additional features arising from plasmon losses and Auger emission are shown to be important. For Lu${\mathrm{H}}_2$, the $4f$ photoionization cross section is determined, and the probability of bulk-plasmon excitations is shown normalized to the $4f$ cross section.