Catalysts based on the first-row (3d) transition metals are commonly seen in chemical and biological reactions. To understand the role of the transition metal in the catalyst, the element specific technique core level spectroscopy is used to probe the electronic structure and geometric properties centered around the metal site. Different types of X-ray spectra can be applied to probe the metal 3d character orbitals involved in reactions, which make it possible to identify and characterize the reactive sites of samples in different forms. A detailed interpretation and understanding of the different X-ray spectra requires a unified method which can be used to model different types of X-ray spectra, e.g., soft and hard X-rays. In this project, the restricted active space method (RAS) will be used to simulate and interpret different types of X-ray spectra by including all important spectral effects: multiplet structures, spin-orbit coupling, charge-transfer excitations, and ligand field splitting.
In the RAS calculation, most important orbitals are included in active space, not only the metal character 3d molecular orbitals (MOs), but also the important ligand MOs. All the spectra calculations can be performed with MOLCAS program. The active space could be designated as RAS(l, m, n; i, j, k), where i, j, and k are the number of orbitals in RAS1, RAS2, and RAS3 spaces respectively, l is the total number of electrons in the active space, m the maximum number of holes allowed in RAS1, and n the maximum number of electrons in RAS3. The electron excitation can be restricted by specifying the minimum number of hole in RAS 1 or the maximum number of electrons in RAS3.