Many-body calculation of the valence photoemission spectrum of Fe(CO)5

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Abstract
The valence photoemission spectrum of Fe(CO)5 is calculated by the ADC(3) Green’s function method. The overall agreement with the experiment is good. It is shown that the quasiparticle picture (QPP) for the outer and inner valence levels (except the 8a‘2 level) derived primarily from CO ligand orbitals breaks down completely due to the one‐hole/two‐hole–one‐particle (1h/2h1p) charge transfer (CT) coupling in the bonded system. Compared to Ni(CO)4 the many‐electron effect is much stronger in Fe(CO)5. In Cr(CO)6 and Fe(CO)5 the 3d shell is incompletely filled, but in contrast to Cr(CO)6 in Fe(CO)5 there is no significant contribution from the local metal excitations. It is shown that for the 8a■2 level the 1h state is still more stable than the 2h1p states. Consequently the main line (with an intensity of 0.76) is interpreted as the 1h state where the screening charge resides on the bonding orbital which is more polarized toward the ligand than in the ground state. The satellites are dominated by 2h1p configurations where the bonding to antibonding shake‐up excitations occur. For the other CO derived levels the strong mixing of 1h and 2h1p configurations leads to the breakdown of the QPP of the ionization and thus a distinction between main line and satellite line becomes meaningless. For most of the levels, the strong dynamical metal–ligand CT hole–particle excitations, where the creation of two holes in the same metal orbital is involved, lead to the breakdown of the QPP of the ionization. A similar strong many‐electron effect is also found in Cr(CO)6. For most of the outer and inner valence levels of these molecules, the QPP of the ionization breaks down.