Ionized and excited states of ferrocene: Symmetry adapted cluster-configuration-interaction study

The ground state, singlet, and triplet excited states, and ionized states of ferrocene Fe(C5H5)(2) were studied by the symmetry adapted cluster (SAC)/SAC-configuration-interaction method. The calculated ionization energies and intensities fairly well reproduced the observed photoelectron spectrum in the wide region of 6-14 eV. In particular, the first two peaks (E-2(2)' and (2)A(1)(')) were assigned to the ionizations from the occupied 3d orbitals of Fe, mixed already with the two-electron shake-up processes. This is the first ab initio quantitative assignment that is consistent with the experimental data. For the singlet states, three d-d transitions were calculated at 2.12, 2.26, and 4.02 eV, which correspond to the experimental peaks observed at 2.69, 2.97, and 3.82 eV. We propose possible assignments for other absorption bands in the range of 2.12-6.57 eV. In another three triplet d-d transition states we calculated, we found that the energy order of these states (1 E-3(1)', 1 E-3(2)', 2 E-3(1)') differs from that of singlet states (1 E-1(2)', 1 E-1(1)', 2 E-1(1)'). (C) 2002 American Institute of Physics.