High resolution HeI and HeII photoelectron spectra of the thallium halides: valence bands and Tl 5d ligand field splittings

Abstract

We report high resolution photoelectron spectra of both the valence bands and Tl 5d levels of the thallium halides (TlX; X = Cl, Br, I) in the gas phase. A transition state Xα-SW calculation on TlCl agrees with previous valence band assignments, although our calculated orbital characters are quite different from those reported previously. The calculated spin–orbit splitting of the 22II state in TlI is in good agreement with the observed value of 0.83 eV. Line width variations are rationalized considering the increase in covalency from TlCl to TlI, and variations in the slope of the excited state potential curve.Ligand field splitting of the Tl 5d level has been resolved in all three compounds. The observed values of the non-cubic part of the crystal field (C20) are: −0.0210 eV (TlCl), −0.0233 eV (TlBr), and −0.0258 eV (TlI). The above trend is due to the increasing covalency from TlCl to TlI, with a concomitant increase in the Tl 6p orbital population. Calculated C20 values are in good agreement with those observed. The configuration interaction structure in the Tl 5d region is explained qualitatively using Xα-SW calculations of two-hole valence band energies in TlCl.