X-RAY-ABSORPTION NEAR-EDGE SPECTROSCOPY (XANES) AT THE PHOSPHORUS K-EDGE OF TRIORGANOPHOSPHINESELENIDES

The usefulness of XANES measurements for analysing the local environme nt of the absorbing atom is demonstrated at the P K-edge for some trio rganophosphineselenides. Using XANES as a fingerprint method, informat ion about the influence of the first and higher coordination shells on the XANES spectra have been obtained. We demonstrate once again an in fluence of the electronegativity of the substituents bound to the abso rbing atom on the spectre. Furthermore, we show that an aromatic subst ituent in the first coordination shell strongly influences the shape o f the XANES resonances as compared to an aliphatic substituent. This i s evident in a splitting of the white line, if the aromatic substituen t is directly bound to the absorbing atom. In this case, the formation of a delocalized pi-electron system is possible, which shortens the P -C-aryl bond length because of its positive mesomeric effect. These re sults are supported by MS X alpha-calculations.