Photoelectron Spectra of Solid Inorganic and Organometallic Compounds Using Synchrotron Radiation. Valence Band Spectra and Ligand Field Broadening of Core d Levels

Abstract

Using synchrotron radiation from the Wisconsin storage ring as the photon source, we have obtained valence band and outermost d core level photoelectron spectra of a number of solid Sn, In, Sb, and Pb organometallic and inorganic compounds containing phenyl (Ph), methyl (Me), chloride, and acetylacetonates (AcAc, BzAc, BzBz) as ligands. With a total instrumental resolution of 0.3 eV at 57 eV photon energies, we have obtained d core line widths in the low 0.7 eV region, within 0.15 eV of the corresponding metal line widths. Correlations of the Sn 4d line widths and chemical shifts with previously obtained 3d widths and shifts show that we have minimized experimental difficulties such as charging and decomposition. The resolution in the valence band region is good enough to detect and assign a large number of the valence band peaks. For example, eight valence band peaks can be resolved in the Ph4Sn spectrum, and these peaks can be assigned readily to the benzene molecular orbitals and the Sn-C bonding orbitals. The routinely variable photon energy is sometimes useful for assigning peaks in these spectra. The broadening of the Sn 4d peaks is attributed to an unresolved ligand field splitting. In particular, the broadening is due to the asymmetry or electric field gradient C20 term in the crystal field expansion. From the known nuclear field gradients, the magnitude of the C20 term (-0.036 ± 0.006 eV) in the Me2Sn compounds is shown to be consistent with the |C20| values observed previously for Me2Cd (0.026 eV), XeF2 (0.042 eV), and XeF4 (0.043 eV). These results show that the electric field gradient splitting has to be considered as an important broadening mechanism (and splitting mechanism at very high resolutions) in photoelectron and adsorption studies. The 4d and 5d spin-orbit splittings do not vary with the chemical environment. However, the ratio of the d5/2:d3/2 intensities appears to be sensitive to the chemical environment and varies considerably from the theoretical 1.5:1 ratio expected in an independent particle picture. © 1977, American Chemical Society. All rights reserved.