On the complex structure of the optical spectra of a tetragonal calomel single crystal in a wide energy range

The spectral complex of optical functions of the calomel Hg$_{2}$Cl$_{2}$ single crystal is determined in the range 0–20 eV at 300 K in unpolarized light. The spectra of the imaginary part of the permittivity $\varepsilon_{2}(E)$, the bulk $-{\operatorname{Im}}\varepsilon^{-1}$ and the surface $-{\operatorname{Im}}(1+\varepsilon)^{-1}$ electron energy losses are decomposed into elementary bands. Their main parameters, including energies and oscillator strengths of the transition bands are determined. Calculations are performed on the basis of the experimental reflectance spectrum of the crystal cleavage. Computer programs based on Kramers–Kronig relations, analytical formulas, and the advanced parameterfree method of combined Argand diagrams are used. The main features of the spectral set of optical functions and the parameters of expansion band components $\varepsilon_{2}(E)$, $-{\operatorname{Im}}\varepsilon^{-1}$, and $-{\operatorname{Im}}(1+\varepsilon)^{-1}$ are determined.