Optical properties of Rh, Pd, Ir, and Pt

The reflectivity and ${\epsilon }_2$ spectra of the fcc metals Rh, Pd, Ir, and Pt are reviewed and discussed between about 0.1 and 30 eV. Structures in ${\epsilon }_2$ are interpreted in terms of recent band calculations. Calculations of the joint density of states and ${\epsilon }_2$, based on the energy distribution of the joint-density-of-states results of Smith, are presented and compared with experiment. The low-energy dielectric functions are observed to be sensitive to the bands near the symmetry point $L$, notably the spin-orbit-split $d$-like states which shift relative to the $\mathrm{sp}$-like $L_6^{-}$ level and affect transitions below about 2 eV. Structure near 2.8 eV in Rh is interpreted in terms of transitions between bands 3 and 5 along $Q$. Like the bcc and hcp transition metals, the fcc metals display minima in ${\epsilon }_2$ near 10 eV and, at higher energies, characteristic structures are observed which can be understood qualitatively in terms of transitions to high-lying bands. The fcc metals, like the bcc and hcp transition metals, are shown to have two volume and two surface plasmons. In the discussion, shortcomings and uncertainties in the optical data are pointed out and appeals for further study are made.