Valence ionized states of iron pentacarbonyl and η5-cyclopentadienyl cobalt dicarbonyl studied by symmetry-adapted cluster-configuration interaction calculation and collision-energy resolved Penning ionization electron spectroscopy

Abstract

Valence ionized states of iron pentacarbonyl Fe(CO)(5) and eta(5)-cyclopentadienyl cobalt dicarbonyl Co(eta(5)-C(5)H(5))(CO)(2) have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy (2D-PIES), and symmetry-adapted cluster-configuration interaction calculations. Theory provided reliable assignments for the complex ionization spectra of these molecules, which have metal-carbonyl bonds. Theoretical ionization energies agreed well with experimental observations and the calculated wave functions could explain the relative intensities of PIES spectra. The collision-energy dependence of partial ionization cross sections (CEDPICS) was obtained by 2D-PIES. To interpret these CEDPICS, the interaction potentials between the molecules and a Li atom were examined in several coordinates by calculations. The relation between the slope of the CEDPICS and the electronic structure of the ionized states, such as molecular symmetry and the spatial distribution of ionizing orbitals, was analyzed. In Fe(CO)(5), an attractive interaction was obtained for the equatorial CO, while the interaction for the axial CO direction was repulsive. For Co(eta(5)-C(5)H(5))(CO)(2), the interaction potential in the direction of both Co-C-O and Co-Cp ring was attractive. These anisotropic interactions and ionizing orbital distributions consistently explain the relative slopes of the CEDPICS.

Resonant photoemission at the iron M-edge of Fe(CO)5

“…This indicates a smaller fraction of the Auger contributions to bands B and C. The overlap of the continuum wavefunctions, ρ α 2 , is also considerably smaller in bands B and C than in band A. In their quantum chemistry calculations, Fukuda et al 3 estimated the Fe-character of the 10e to be 77%. We use this value to calibrate the relative A α values to the Fecharacter and include the values in Table I.…”

“…The features between 8.5 and 10.5 eV (band A) are attributed to the 10e and 3e molecular orbitals, which are principally Fe 3d in character. 3,5 The photolines above 14 eV are typically attributed to the ligands. 5,2, 3 Baerends et al 2 and Fukuda et al 3 assigned the photolines between 13 and 17 eV (band B) to the CO(5σ ) and CO(1π ) orbitals, and those from 17 and 20 eV (band C) to the CO(4σ ) orbital.…”

“…3,5 The photolines above 14 eV are typically attributed to the ligands. 5,2, 3 Baerends et al 2 and Fukuda et al 3 assigned the photolines between 13 and 17 eV (band B) to the CO(5σ ) and CO(1π ) orbitals, and those from 17 and 20 eV (band C) to the CO(4σ ) orbital. The broad peaks centered around 20.5 eV and 23.9 eV binding energy are the shake-up satellites of bands B and C, respectively.…”

“…5 and 3 are calculated with different methods, showing a spread of up to 2 eV, leaving space for some uncertainty and indeed the two papers do not agree in their assignment of the experimental photolines to calculated transitions. Fukuda et al 3 base their assignment not only on an energetic argument but also on calculated monopole strength and a Penning ionization study. For comparison, the orbital assignments from both Refs.…”

“…A comparison of calculations with electron energy resolved 2, 3 and ionization-yield experiments 4 of Fe(CO) 5 attributes the detected photolines above 13 eV to energy levels with predominant ligand character. 3,5 Resonant photoemission in transition metal atoms and transition metal-containing molecules has been a topic of close study since the first observation of resonant photoemission in Ni metal in 1977. 6 As the photon energy is swept through resonance with the np→nd absorption threshold, a Fano resonance 7 is observed in the nd electron emission signal.…”