Electronic structures of the ground and excited states of Mo(CO)6: SAC-CI calculation and frozen orbital analysis

The symmetry adapted cluster (SAC) and symmetry adapted cluster–configuration interaction (SAC-CI) many body theories have been applied to calculate ground-and excited-state energies, and oscillator strengths of Mo(CO)₆. The experimental spectrum of Mo(CO)₆ is well reproduced by the present study, which is the first ab initio study of the excited states including electron correlations. The lower excited states are characterized as the metal-to-ligand chargetransfer (MLCT), ligand field transition (LFT) and Rydberg excitations. The LFT states are calculated to be much higher than the experimentally expected values. A new assignment based on the present calculations is proposed. The frozen orbital analysis (FZOA) method is applied to rationalize clearly the physical basis of the ordering of the excited states. This analysis is shown to be useful for understanding the excitation levels.