Interpretation of the valence photoelectron spectra of Mn(CO)5H, Mn(CO)5CH3 and Fe(CO)4H2

Abstract

The valence photoelectron spectra of Mn(CO)₅H, Mn(CO)₅CH₃ and Fe(CO)₄H₂ are found to be incorrectly interpreted using Koopmans' theorem in conjunction with ab initio wavefunctions. The relative ordering of the ionic states arising from the metal 3d and Mn—X (X = H, CH₃)σ-bonding orbitals given by Koopmans' theorem is opposite to that observed experimentally. Such a breakdown in Koopmans' theorem is discussed in terms of the orbital relaxation accompanying ionization from the metal and from the ligand orbitals. The use of CNDO wavefunctions to interpret the measured ionization potentials is also examined.