Intensities in the x-ray photoelectron spectra and electronic structures of the oxyanions of Si, P, S, Cl, Mn, and Cr

Abstract

X‐ray photoelectron spectra of the valence region of the lithium salts of ${\mathrm{SiO}}_4^{\text{4−}}\mathrm{,\hspace{0.17em}}{\mathrm{PO}}_4^{\text{3−}}\mathrm{,\hspace{0.17em}}{\mathrm{SO}}_4^{\text{2−}}\mathrm{,\hspace{0.17em}}{\mathrm{ClO}}_4^{-}\mathrm{,\hspace{0.17em}}{\mathrm{ClO}}_3^{-}\mathrm{,\hspace{0.17em}}{\mathrm{ClO}}_2^{-}\mathrm{,\hspace{0.17em}}{\mathrm{SO}}_3^{\text{2−}}\mathrm{,\hspace{0.17em}}{\mathrm{S}}_2{\mathrm{O}}_3^{\text{2−}}\mathrm{,\hspace{0.17em}}{\mathrm{MnO}}_4^{-}$ , and ${\mathrm{CrO}}_4^{\text{2−}}$ have been measured. With the aid of molecular orbital calculations and available x‐ray fluorescence data an assignment is given of the photoelectron lines. The line intensities are analyzed with the aid of an LCAO‐type model that relates the molecular‐orbital photoionization cross sections to atomic‐orbital photoionization cross sections and atomic populations in the molecular orbitals. The required atomic cross sections have been obtained from the valence photoelectron spectra of MgO, LiCl, S, P, and Si. The intensity model is shown to give a satisfactory interpretation not only of the trends in the spectra but also of the absolute intensities. Both intensities and energies of the high‐binding‐energy photoelectron lines demonstrate that the contribution of the oxygen 2s orbitals to the bonding in the main group oxyanions increases with increasing atomic number of the central atom and is especially important in the ${\mathrm{ClO}}_n^{-}$ anions. The increase in the e, 3t₂ − t₁ energy splitting from ${\mathrm{SiO}}_4^{\text{4−}}$ to ${\mathrm{ClO}}_4^{-}$ is due to increased π backbonding between the oxygen 2p and central atom 3d orbitals. The intensities of the low‐binding‐energy lines of ${\mathrm{CrO}}_4^{\text{2−}}$ and ${\mathrm{MnO}}_4^{-}$ show that the e and 3t₂ orbitals of these anions have appreciable metal 3d character.