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Ferrous (Fe 2+ ) and ferric (Fe 3+ ) compounds were investigated by XPS to determine the usefulness of calculated multiplet peaks to fit high-resolution iron 2p 3/2 spectra from high-spin compounds. The multiplets were found to fit most spectra well, particularly when contributions attributed to surface peaks and shake-up satellites were included. This information was useful for fitting of the complex Fe 2p 3/2 spectra for Fe 3 O 4 where both Fe 2+ and Fe 3+ species are present. It was found that as the ionic bond character of the iron -ligand bond increased, the binding energy associated with either the ferrous or ferric 2p 3/2 photoelectron peak also increased. This was determined to be due to the decrease in shielding of the iron cation by the more increasingly electronegative ligands. It was also observed that the difference in energy between a high-spin iron 2p 3/2 peak and its corresponding shake-up satellite peak increased as the electronegativity of the ligand increased. The extrinsic loss spectra for ion oxides are also reported; these are as characteristic of each species as are the photoelectron peaks.

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The binary transition-metal monophosphides CrP, MnP, FeP, and CoP have been studied with X-ray photoelectron spectroscopy. The shifts in phosphorus 2p(3/2) core line binding energies relative to that of elemental phosphorus indicated that the degree of ionicity of the metal-phosphorus bond decreases on progressing from CrP to CoP. The metal 2p(3/2) core line binding energies differ only slightly and show similar line shapes to those of the elemental metals, reaffirming the notion that these transition-metal phosphides have considerable metallic character. The satellite structure observed in the Co 2p(3/2) X-ray photoelectron spectra of Co metal and CoP was examined by reflection electron energy loss spectroscopy and has been attributed to plasmon loss, not final state effects as has been previously suggested. Valence-band spectra of the transition-metal phosphides agree well with the density of states profiles determined from band structure calculations. The electron populations of the different electronic states were extracted from the fitted valence-band spectra, and these confirm the presence of strong M-P and weak P-P bonding interactions. Atomic charges determined from the P 2p core line spectra and the fitted valence-band spectra support the approximate formulation M(1+)P(1-) for these phosphides.

The electronic structures of metal-rich binary phosphides M 2 P and M 3 P (M ) Cr-Ni) have been examined by means of X-ray photoelectron and absorption spectroscopy and compared with those of the monophosphides MP. The P 2p 3/2 binding and P K-edge absorption energies decrease with greater ionic character of the M-P bonding and indicate the presence of anionic phosphorus, contrary to previous theoretical assertions but consistent with our previous results. Interatomic effects play a more important role in affecting the energy shifts in these metal-rich phosphides than in the monophosphides, becoming more pronounced with higher metal concentration. Although the M 2p 3/2 XPS spectra show no discernible shifts in binding energies, they reveal satellite features whose intensity can be related to metal charge in the Co-and Ni-containing phosphides. In these cases, the metal charge becomes less positive with higher metal concentration. For Ni 2 P and Ni 3 P, this trend was confirmed from an analysis of the Ni L-edge and M-edge XANES spectra.