2P-]3D EXCITATIONS IN TRANSITION-METAL COMPOUNDS - A COMPUTATIONAL INVESTIGATION ON FE(CO)5, FE(C5H5)2 AND CR(CO)6

Ab initio calculations of the metal 2p excitation spectra of Fe(CO)5, Fe(C5H5)2 and Cr(CO), are presented. The results are discussed and com pared with available experimental data and previous theoretical result s obtained for related carbonyl compounds. The calculated spectra show a strong sensitivity to the nature of the ligand and the bonding situ ation but, in the case of complexes with the same type of attached lig and, also to the molecular symmetry and the formal d count of the meta l atom. The correlation between the spectral features and the theoreti cal attribution of the excited states is analysed by means of appropri ate MO energy level diagrams indicating the potential of the technique for obtaining detailed information on the nature of the metal-ligand bond. The good agreement between the theoretical and experimental spec tra strongly supports the adequacy of the relatively simple computatio nal scheme adopted for the calculations, provided due care is paid to an accurate treatment of the strong relaxation present in such systems , allowing a precise analysis of the experimental data for moderately sized systems.