Variable photon energy photoelectron spectroscopy of tris-cyclopentadienyl lanthanides

Marcello Coreno,Nikolas Kaltsoyannis,Andrea Sella,Naima Narband,Rosemary Coates,Jennifer C Green,Charlene Hunston,Monica De Simone

doi:10.1039/c3dt53512f

Abstract

The gas phase photoelectron (PE) spectra of LnCp3 (Cp = η-C5H5; Ln = Pr, Nd, Sm), measured with a wide range of photon energy, are reported. Resonances observed in the photon energy regions of 4d to 4f excitation enable identification of ion states resulting from 4f ionization. For all three compounds molecular ion states characteristic of both 4f(n) and 4f(n-1) configurations are observed (Pr, n = 2; Nd, n = 3; Sm, n = 6). The molecular ion ground states have a hole in the uppermost ligand orbital of a' symmetry and are reached by either ligand or f electron ionization. The results are discussed in the context of the previously reported spectra of the Ce, Yb and Lu analogues. For YbCp3 f orbital/ligand interaction is proposed in the molecular ground state and for CeCp3(+) in the molecular ion ground state. For PrCp3 and NdCp3 final state effects are proposed as the origin of the dual configuration structure in their PE spectra. When the contributing orbitals are close in energy the 4f/a' interaction can give rise to significant covalent bonding even in the absence of effective overlap.

Highlights

Marcello Coreno,a Monica de Simone,b Jennifer C
Resonances observed in the photon energy regions of 4d to 4f excitation enable identification of ion states resulting from 4f ionization
The 4f cross sections have a delayed maximum in the photon energy region between 75 and 150 eV depending on the particular lanthanide

Summary

Introduction

Marcello Coreno,a Monica de Simone,b Jennifer C. Resonances observed in the photon energy regions of 4d to 4f excitation enable identification of ion states resulting from 4f ionization. Core ionization may result in significant perturbation of a molecule’s electronic structure, which manifests itself in satellite structure accompanying the primary core PE bands, often referred to as shake-up or shake-down bands These bands are assigned to many electron processes in which a valence excitation or transition accompanies the core ionization. Ionization of the 4f electrons of lanthanides gives very characteristic final state structure that depends on the electronic ground state adopted by the 4f n configuration. The cross sections of s and p bands have maxima close to threshold, employing incident photon energies away from p based maxima yet near to 4f maxima will enable unambiguous characterization of the final state structure. In a PE experiment, with careful selection of photon energies, as is enabled by synchrotron radiation, ion states accessible by f ionization may be distinguished from those accessible by ligand ionization

Results

Discussion

Conclusion