K. Godehusen

Open shells and multi-electron interactions: core level photoionization of the 3d metal atoms

This review covers the outer core level photoionization of the free 3d metal atoms from Sc to Cu. The experimental 3p, 3s and 2p photoemission and photoabsorption spectra are discussed. A comparison emphasizes common features and distinct differences. The interpretation of the data based on ab initio calculations reveals the influence of multi-electron interactions in the 3d metal atoms. We focus on the fundamental effects and main interactions which govern the electronic structure of these open shell atoms. (Some figures in this article are in colour only in the electronic version)

Iron L-Edge Absorption Spectroscopy of Iron Pentacarbonyl and Ferrocene in the Gas Phase

Fe L-edge X-ray absorption spectra of gas-phase iron pentacarbonyl and ferrocene measured in total-ion yield mode are reported. Comparison to previously published spectra of free iron atoms and gaseous iron chloride demonstrates how the interplay of local atomic multiplet effects and orbital interactions in the metal-ligand bonds varies for the different systems. We find changes in the degree of metal-ligand covalency to be reflected in the measured 2p absorption onset. Orbital- or state-specific fragmentation is furthermore investigated in iron pentacarbonyl and ferrocene by analyzing the partial-ion-yield spectra at the Fe L-edge. Strong dependence of the yields of different fragments is observed in ferrocene in contrast to iron pentacarbonyl. This difference is attributed to the different degrees to which the 2p core hole is screened in the two systems and to which charge is rearranged in the Auger final states. We provide experimental benchmark spectra for new ab initio approaches for calculating metal L-edge absorption spectra of metal complexes.

Resonant 3p photoelectron spectroscopy of free Cu atoms

Excitation and decay of the Cu 3p core resonances have been studied by resonant photoelectron spectroscopy. In comparison with theoretical predictions the importance of electron correlation for the resonance energies and line shapes is verified.

Resonant inner-shell photoelectron spectra of ground-state and laser-excited Cr atoms

Photoelectron spectra and partial cross sections of ground-state and laser-excited Cr atoms in the range of the excitations are presented. The experimental spectra are compared with results obtained by calculations within the spin-polarized random-phase approximation with exchange (SP RPAE), in which the dynamic relaxation upon core hole creation is taken into account.

Photoionization of Ca atoms in a time resolved pump-probe experiment with synchronized undulator- and Ti:Saphir laser pulses

Abstract In this Letter we describe an experiment to synchronize ps-pulses from a modelocked Ti:Saphir laser with 83.33 MHz pulses from the BESSY storage ring. To demonstrate the method, Ca atoms has been ionized in a pump probe experiment. The atoms were excited in the intermediate state with the frequency doubled laser radiation and probed with the BESSY undulator radiation. Changing the delay between the pulses we observed the dependence of the electron yield. The time resolution we achieved is in the order of 1 ns.

Linear dichroism in the 4d photoionization of atomic europium

The dichroism in the 4d photoelectron spectra of laser polarized Eu atoms has been determined with linearly polarized soft x-ray radiation. The results are discussed in comparison with the predictions by the LS-coupling model and by configuration interaction Hartree-Fock calculations, thereby demonstrating the strong influence of valence electron correlations. The interpretation of the dichroism in the 4d photoelectron spectra of solid Gd in terms of an ionic model is corroborated by the close similarity of the Gd solid and the Eu atom spectra.

Breakdown of the three-parameter model for the dichroism in the 4f photoelectron spectrum of laser-aligned Eu atoms

The dichroism in the 4f photoelectron spectra of laser-aligned Eu atoms has been determined with linearly polarized vacuum ultraviolet radiation. The experimental results disagree with the prediction of the three-parameter model based on the absolute magnitude and relative phase of the 4f d, g transition matrix elements. It is suggested that strong configuration interactions, confirmed in high-resolution photoelectron spectra, are the cause of the breakdown of the three-parameter model.

LINEAR DICHROISM IN PHOTO-INDUCED AUGER ELECTRON EMISSION FROM ALIGNED CR ATOMS

We report the first observation of linear dichroism in the photo-induced Auger electron emission from aligned atoms. The linear dichroism in the Cr Auger spectrum shows striking similarity to the corresponding linear dichroism in the 3p photoelectron spectrum. The theoretical analysis presented here proves that the linear dichroism in the Auger spectrum depends on the same dynamical parameters as the linear dichroism in direct photoionization.

Linear dichroism in the core-resonant photoelectron spectra of laser-aligned Cr atoms

The linear dichroism in the intensity of the electrons (LD) emitted by laser-aligned ground state and excited-state Cr atoms has been exploited in order to characterize the prominent 3p core resonances. The experimental spectra are compared to calculations based on theoretical partial cross sections.

Ultrafast Temperature Jumps in Liquid Water Studied by Infrared-Pump and X-ray Absorption-Probe Spectroscopy

We report the first time-resolved x-ray absorption study of liquid water. Structural changes in the hydrogen-bond network as induced by resonant femtosecond-infrared excitation are monitored via transient x-ray absorption at the oxygen K-edge.