title: A mystery solved? Photoelectron spectroscopic and quantum chemical studies of the ion states of CeCp3(+).
abstract: The electronic states of CeCp(3)(+) have been studied experimentally by variable photon energy photoelectron spectroscopy, and computationally using multi-configurational ab initio methods. Relative partial photoionisation cross section and branching ratio data are presented to confirm our previous conclusion that bands A and D in the valence photoelectron spectrum, despite their 3.2 eV separation, are produced by ionization of the single 4f electron of CeCp(3) [M. Coreno, M. de Simone, J. C. Green, N. Kaltsoyannis, N. Narband and A. Sella, Chem. Phys. Lett., 432, 2006, 17]. The origin of this effect is probed using the CASSCF/CASPT2 approach. While configurations based on the canonical CASSCF orbitals are found to be an unreliable description of the ground and excited states of CeCp(3)(+), the state-specific natural orbitals and their occupations yield greater insight, allowing us to characterize ion states in terms of the presence or otherwise of a Ce 4f-localised electron. Neither the CeCp(3)(+) ground state (assigned to band A), and two excited states ((1)A' and (1)A'', associated with band D), possess such a metal-based electron, as expected of f ionization. The (1)A' and (1)A'' states differ from the ground state in having a significant Ce 5d population, arising from Cp --> Ce charge transfer, which accompanies f ionization, and which is responsible for the energetic separation of bands A and D in the valence photoelectron spectrum.
authors.affiliation: Department of Chemistry, University College London, 20 Gordon Street, London, UK WC1H 0AJ.
authors.forename: Rosemary
authors.initials: R
authors.lastname: Coates
authors.forename: Marcello
authors.initials: M
authors.lastname: Coreno
authors.forename: Monica
authors.initials: M
authors.lastname: DeSimone
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Green
authors.forename: Nikolas
authors.initials: N
authors.lastname: Kaltsoyannis
authors.forename: Andrew
authors.initials: A
authors.lastname: Kerridge
authors.forename: Naima
authors.initials: N
authors.lastname: Narband
authors.forename: Andrea
authors.initials: A
authors.lastname: Sella