Titanium core-level spectra in titanium tetrahalide molecules

Molecular-orbital calculations of ${\mathrm{TiF}}_4$, ${\mathrm{TiCl}}_4$, ${\mathrm{TiBr}}_4$, and ${\mathrm{TiI}}_4$ molecules have been made with use of self-consistent local-density theory with the discrete variational (DV-Xα) method. Core-level excitation energies corresponding to x-ray photoelectron spectroscopy (XPS) measurements are calculated. Spectral peaks associated with metastable final states of the core ionized atom that include relaxation and charge transfer processes are calculated. XPS spectra of Ti core levels in these compounds show that binding energies of both main lines and satellites clearly depend on the ligated anion. The observed systematic behavior of ionization potentials and satellite separation energies for the halide series is calculated with reasonable accuracy. With use of the single-determinant formalism, contributions to the intensity of the main line and satellites are examined.