CRYSTAL-FIELD SPLITTINGS OF CONTINUUM D-ORBITALS - A COMPARATIVE-STUDY ON THE L2,3 EDGE X-RAY ABSORPTION-SPECTRA OF SI, P AND S COMPOUNDS

High resolution P 2p photoabsorption spectra of PF5, POF3 and POCl3 have been obtained using monochromatized synchrotron radiation. The assignment of the spectra is assisted with theoretical local density functional multiple scattering (MS-Xalpha) calculations of the absorption cross sections. The post-edge features are found to be dominated by electronic excitations to quasi-bound 3d orbitals. A survey of the 2p post-edge spectra of related Si, P and S compounds show that these resonant structures correlate very well with that of the d orbital splittings under the interactions of the electrostatic field of the ligands. Although details of the mechanisms are not exactly the same, the classical crystal field theory correctly predicts the symmetries and energy ordering of the transitions to the excited 3d orbitals. The pre-edge region of the P 2p spectra are very rich in features and can be assigned to excitations to antibonding and Rydberg orbitals. Our calculation also shows that the P s and d compositions mixed into an unoccupied orbital are the factors determining the intensity of transition from P 2p to the specific unoccupied orbital.