title: Kβ X-ray emission spectroscopy offers unique chemical bonding insights: revisiting the electronic structure of ferrocene.
abstract: Kβ X-ray emission spectroscopy (XES) is emerging as a powerful tool for the study of chemical bonding. Analyses of the Kβ XES of ferrocene (Fc) and ferrocenium (Fc(+)) are presented as further demonstrations of the capabilities of the technique. Assignments of the valence to core (V2C) region of these spectra as electric dipole-allowed cyclopentadienyl (Cp) → Fe 1s transitions demonstrate that XES affords electronic structural insight into the energetics of ligand-based molecular orbitals (MOs). Combined with K-edge X-ray absorption spectroscopy (XAS), we show that XES can provide analogous information to photoemission spectroscopy (PES). Density functional theory (DFT) analyses reveal that the V2C transitions in Fc/Fc(+) derive their intensity from Fe 4p admixture (on the order of 5-10%) into the Cp-based MOs from which they originate. These 4p admixtures confer bonding character to the Cp-based a(2u) and e(1u) MOs to at least the extent of backbonding contributions to frontier MOs from higher-lying Cp π* MOs.
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA. kml236@cornell.edu
authors.forename: Kyle M
authors.initials: KM
authors.lastname: Lancaster
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Finkelstein
authors.forename: Serena
authors.initials: S
authors.lastname: DeBeer
mesh_terms: D001665:Binding Sites; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry*; D000075163:Metallocenes; D015394:Molecular Structure; D011789:Quantum Theory; D013052:Spectrometry, X-Ray Emission
chemical_list: D005296:Ferrous Compounds; D000075163:Metallocenes; C004998:ferrocene