Many-body calculation of the valence photoemission spectrum of Cr(CO)6

The valence photoemission spectrum of Cr(CO${)}_6$ is calculated by the third-order algebraic-diagrammatic-construction Green’s-function method. The overall agreement with experiment is good. It is shown that the quasiparticle picture of the levels derived primarily from the CO 1π and 4(5)σ levels begins to break down or breaks down completely due to one-hole (1h) and two hole–one-particle (2h1p) charge transfer (CT) and local metal excitation coupling in the bonded system. Compared to Ni(CO${)}_4$, the many-electron effect in Cr(CO${)}_6$ is much stronger. Because of the incompletely filled 3d shell, there is a significant contribution from the local metal excitations. It is shown that for the 2${\mathit{t}}_{2\mathit{g}}$, 8${\mathit{t}}_{1\mathit{u}}$, 5${\mathit{e}}_{\mathit{g}}$, 1${\mathit{t}}_{1\mathit{g}}$, 1${\mathit{t}}_{2\mathit{u}}$, 7${\mathit{t}}_{1\mathit{u}}$, 8${\mathit{a}}_{1\mathit{g}}$, and 7${\mathit{a}}_{1\mathit{g}}$ levels the 1h state is still more stable than the 2h1p states. Consequently, the main line (with an intensity of 0.6–0.7) 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 1${\mathit{t}}_{2\mathit{g}}$, 4${\mathit{e}}_{\mathit{g}}$, and 6${\mathit{t}}_{1\mathit{u}}$ levels, the strong mixing of 1h and 2h1p configurations leads to the breakdown of the quasiparticle picture of the ionization and thus a distinction between the main line and satellite line becomes meaningless. For the 1${\mathit{t}}_{2\mathit{g}}$ level, the strong 1${\mathit{t}}_{2\mathit{g}}^{\mathrm{-}1}$⇆2${\mathit{t}}_{2\mathit{g}}^{\mathrm{-}2}$3${\mathit{t}}_{2\mathit{g}}$ CT excitation, where the excitations occur in the orbital space of the same symmetry, creating two holes in the same orbital, leads to the breakdown of the quasiparticle picture of the ionization.