Optical Constants of TlCl and TlBr with a Comparison of the Kramers-Kronig and "Two-Angle" Methods of Data Analysis

The optical constants of TlCl and TlBr were determined in the region of 3 to 21 eV from reflectivity measurements. The low-energy measurements confirm the previous work of Zinngrebe. The high-energy structure is consistent with the available information on relative positions of atomic energy levels and with a plasma resonance associated with approximately 8 electrons per molecule. Both the "two-angle" and Kramers-Kronig methods were used in analyzing the data. The assumption of unpolarized radiation for a near-normal incidence monochromator can cause a considerable error in the results. The "two-angle" analysis is more sensitive to this error than the Kramers-Kronig technique, especially in the region of large values of $n$ and $k$. When polarization effects are not important, the "two-angle" method gives results as good as or better than the Kramers-Kronig analysis.