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New journal of physics 18(11), 113007 (2016). doi:10.1088/1367-2630/18/11/113007, The electronic, chemical and magnetic properties of in situ prepared, mass-selected and deposited Co$_x$Rh$_y$ alloy clusters with up to five atoms per cluster have been studied by means of x-ray absorption and x-ray magnetic circular dichroism spectroscopy. The clusters were supported on a remanently magnetized Ni film. The cluster properties exhibit strong size and composition dependent effects. By alloying of pure Co$_{1,2}$ adatoms and dimers with Rh the chemical reactivity towards oxygen is significantly enhanced for specific compositions. The oxidation of the alloyed clusters strongly affects the magnetic properties which results in a reduction of the orbital and spin magnetic moments. The exchange coupling between the oxidized Co atoms and the Ni surface exhibits a size and a composition dependent oscillation between antiferromagnetic and ferromagnetic coupling., Published by IOP, [London]

Nature Communications 9(1), 2259 (2018). doi:10.1038/s41467-018-04740-5, The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H2 two-electron wave function in which electron–electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources., Published by Nature Publishing Group UK, [London]

We present results of an experimental study of magnetic properties of small Ru clusters deposited on a thin Fe film grown on Cu(001) surface. X-ray magnetic circular dichroism (XMCD) measurements show finite spin and orbital moments of Ru dimers and trimers, however a magnetic moment for a Ru monomer has been not observed. A corresponding theoretical study based on the fully relativistic multiple scattering KKR method is presented. Detailed theoretical analysis has been performed to explain the experimental findings. In particular a direct comparison of the calculated XMCD with the experiments suggests diffusion into the surface as a possible reason for the apparent quenching of the spin magnetic moment for Ru monomers.

An almost linear relation between the Pt amount and the orbital to spin moment ratio (μl/μs) has been found in Cox Pt100–x nanoparticles prepared by vapour deposition and possessing a well defined chemically disordered crystallographic structure. X-ray magnetic circular dichroism (XMCD) measurements done at the L2,3Co edges show that a 4.0 nm, x = 100 Co reference sample has a ratio μl/μs = 0.097, comparable to values found for Co thin layers. An increase of the amount of Pt increases the μl/μs value: μl/μs = 0.11 for x = 78, μl/μs = 0.12 when x = 74 and finally, for x = 38 it becomes μl/μs = 0.140. Nanoparticles prepared by chemical synthesis with size proportional to changes of the stoichiometric ratio, from Co25Pt75 to Co50Pt50, show values of the orbital to spin moment ratio compatible with the trend found for the former ones. The samples prepared by chemical synthesis in a diameter range from 4 nm to 8 nm are characterized by a sharp size distribution of 10%. In contrast to the in situ prepared nanoparticles that are oxide free, however, they show a varying degree of surface oxidation depending on the ambient conditions they are exposed to. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic properties of gadolinium clusters deposited on magnetic ultrathin Fe/Cu(100) films have been measured using X-ray Magnetic Circular Dichroism spectroscopy (XMCD). 3d↦4f as well as 4d↦4f absorption spectra are presented and discussed. Changes in the relative peak intensities between the monomer, dimer and the corresponding monoxides are observed for the $4d \to 4f~^8{\rm D}_{7/2}$ multiplets. The comparison with bulk measurements and calculations exhibit a transition from atomic like to bulk like properties.

The performance of the high-resolution monochromator at FLASH, the vacuum ultra-violet free-electron laser at DESY in Hamburg, was investigated. Using different techniques we measured the relative and absolute transmission of the monochromator beamline for FLASH radiation in the fundamental and higher (up to third) harmonics. The focal spot size of the soft x-ray beam at the output of the beamline was determined as well. In addition, a new way of acquiring the resolving power of the monochromator is discussed. This method has also been applied to calibrate the energy scale of the monochromator system with an accuracy of 5 meV at 48 eV photon energy.

Relative cross sections for photoionization of endohedral fullerene ions Lu3N@C80 q+ (q = 1,2,3) have been measured employing the photon-ion merged-beam technique. The investigations include various ionization channels Lu3N@C80 +q→+p (q = 1,2,3 and p = 2,3,4,5,6), in some cases accompanied by fragmentation of the carbon cage. Prominent structures related to the carbon K-shell ionization threshold were observed in the energy range 280–330 eV. These resonance structures have been analyzed in seven product channels and are compared with previously known absorption spectra of several fullerene species. Within the statistical significance of the data, we do not observe any signatures of the N 1s and Lu 3d thresholds in the energy ranges 390–435 eV and 1500–1700 eV, respectively. By comparing the energies for double ionization of Lu3N@C80 + and Lu3N@C80 2+ at the carbon 1s K-shell threshold, we derive a value of 5.0 ± 0.4 °A for the radius of the carbon cage.

We present size dependent spin and orbital magnetic moments of cobalt (Co$_{n}$$^{+}$, 8 ≤ n ≤ 22), iron (Fe$_{n}$$^{+}$, 7 ≤ n ≤ 17), and nickel cluster (Ni$_{n}$$^{+}$, 7 ≤ n ≤ 17) cations as obtained by X-ray magnetic circular dichroism (XMCD) spectroscopy of isolated clusters in the gas phase. The spin and orbital magnetic moments range between the corresponding atomic and bulk values in all three cases. We compare our findings to previous XMCD data, Stern-Gerlach data, and computational results. We discuss the application of scaling laws to the size dependent evolution of the spin and orbital magnetic moments per atom in the clusters. We find a spin scaling law “per cluster diameter,” ~n$^{−1/3}$, that interpolates between known atomic and bulk values. In remarkable contrast, the orbital moments do likewise only if the atomic asymptote is exempt. A concept of “primary” and “secondary” (induced) orbital moments is invoked for interpretation.

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)

The complete valence shell photoelectron spectrum of tetrafluoromethane has been recorded using synchrotron radiation and the observed structure has been interpreted using ionisation energies and relative spectral intensities computed using the third-order algebraic-diagrammatic-construction (ADC(3)) scheme for the one-particle Green’s function and the outer valence Green’s function (OVGF) method. The ADC(3) calculations were performed using both the original variant based on the Dyson equation and the recently proposed non-Dyson scheme. The theoretical predictions for the single-hole ionic states due to outer valence shell ionisation agree satisfactorily with the experimental results. Ionisation from the inner valence 2t2 and 3a1 orbitals is strongly influenced by reorganisation effects and the intensity is spread amongst numerous satellites. Highly resolved spectra have been measured for the C ∼ 2 T 2 and the D ∼ 2 A 1 states, and the vibrational structure has been associated primarily with excitation of the ν 1 + ( a 1 ) mode. However, the analyses also provide evidence for excitation of the Jahn-Teller active ν 2 + ( e ) mode in the C ∼ 2 T 2 state, and the ν 3 + ( t 2 ) mode in the D ∼ 2 A 1 state. Excitation of this latter mode can be explained in terms of vibronic coupling between the C ∼ 2 T 2 and the D ∼ 2 A 1 states. Photoelectron angular distributions and branching ratios have been determined and demonstrate that shape resonances affect the outer valence shell photoionisation dynamics. The experimental results are compared with previous theoretical predictions but a consistent interpretation has not been obtained. The major difficulty concerns the uncertainty in the locations of valence shell transitions into the 5a1 and the 5t2 virtual orbitals.

High-resolution C 1s near edge X-ray absorption fine structure (NEXAFS) spectra of benzene and benzene-d 6 were measured and compared with the results of state-of-the-art density functional theory (DFT) calculations demonstrating excellent agreement. The spectrum below threshold is dominated by four resonances, each two of them with σ- and π-type final-state orbitals. The π-type resonances have been ascribed in previous work unanimously to antibonding valence orbitals while the character of the σ-type resonances is still the subject of discussion. Based on the present theoretical results and the observed vibrational fine structures both σ-type orbitals are assigned to be valence type with minor admixtures of Rydberg character.

Employing electron spectrometry in conjunction with third generation synchrotron radiation (SR), we present a short overview of the 2p photoelectron spectroscopy of free 3d transition metal atoms. In particular, this paper will focus on the late transition metals from Cr to Cu and a comparison of the free atoms to several compound systems. The atomic experimental spectra are compared to theoretical spectra based on Hartree-Fock (HF) and configuration interaction (CI) calculations. In general a good agreement between experiment and theory is found already for single configuration HF calculations and the observed satellites in the atomic 2p photoelectron spectra (PES) can be attributed to a recoupled 3d valence shell. However, for Ni mixing of several configurations in the final state have to be taken into account.

Employing electron spectrometry in conjunction with tuneable synchrotron radiation, we will present a detailed examination of the photoionization dynamics of selected metal vapor atoms. In particular, this paper will focus on the relative partial cross sections of the atomic Li K-shell main and satellite (ionization with excitation) photoelectron lines in the region of the strong 1snln′l′ autoionizing transitions, the atomic Sc 3d, 4s main and satellite photoelectron lines in the region of the 3p→3d giant resonance, and also the atomic Fe 3d, 4s main and satellite photoelectron lines in the same resonance region. Our experimental data for Sc and Fe will be compared to our state-of-the-art calculations based on the superposition of configuration method developed by Cowan (The Theory of Atomic Structure and Spectra. University of California Berkeley Press, Berkeley and Los Angeles, 1981). Our partial cross section measurements for Li and Sc will be complemented with measurements of the angular distribution parameter, β. In addition, our Li data will also be compared with recent R-matrix calculations (Phys. Rev. 57 (1998) 1045). In the case of Fe, we will also address the term dependent behavior of the partial cross sections on resonance. These results will highlight what can be achieved with today's technology and point the way towards future endeavors in the study of the photoionization dynamics of open-shell metal vapor atoms.

An in-depth photoionization study of the inner-valence electrons in HCl and DCl has been performed using synchrotron radiation. A series of photoelectron spectra of HCl were obtained at a resolution of 23 meV over the binding energy range 25-30.5 eV at various excitation energies and at two different electron collection angles relative to the plane of polarization of the undulator radiation. In addition, photoelectron spectra of DCl were recorded at two different excitation energies. These spectra were compared directly with the threshold photoelectron spectra of HCl and DCl that were recorded previously under similar resolution conditions (similar to30 meV). This comparative study reveals new information on the nature of the numerous band systems observed in this binding energy region. In addition, we present the experimental confirmation of the theoretical prediction given by Andersson et al (2001 Phys. Rev. A 65 012705) that a vibrational progression showing interference structure would appear in the main inner-valence ionization band in the photoelectron spectrum of DCl at a resolution of 10 meV.

Xenon spectra involving emission from ion species of Xe7+ to Xe12+ were analyzed for a plasma focus discharge developed for extreme ultraviolet lithography. Low and higher resolution spectra were recorded in the 8–21 nm wavelength region for different operating conditions and different He–Xe gas mixtures. The spectra have been compared with Hartree–Fock calculations. The modeling included the distribution of the various xenon ion levels at a given electron equilibrium temperature and plasma opacity effects. Spectral analysis showed that the 4d–5p transition arrays are fairly well separated in wavelength for the ions Xe8+ to Xe11+. Good agreement between experiment and calculations was obtained for line positions and intensities, in particular, for the wavelength region at around 13.5 nm.

In this letter, high resolution, ion-charge resolved photoabsorption spectra of free ground state chromium atoms are presented. Using a time-of-flight spectrometer the ion yield of Cr1+ and Cr2+ in the 3p resonance region was recorded. These final-charge separated spectra reveal features that have not been seen before. The double ionization signal shows a stepwise increase at the 3p direct ionization threshold, resulting from spin-dependent decay channels into the final ionic states. Several resonances show different line shapes in both ionization channels; in particular a newly observed Rydberg series exhibits a reversal of its asymmetric Fano profiles.

Using the atomic beam technique and photon excitation with monochromatized synchrotron radiation, the photoelectron spectra from the decays of the 2p → nd resonances of atomic Sc in the region between 397 and 410 eV were investigated. The analysis of the photoelectron spectra was performed with Hartree–Fock calculations for the excitation and the decay of the 2p resonances. Good agreement between experimental and theoretical spectra enabled us to assign the main structures of the spectra to definite transitions, with the participation of electrons from the inner 3s and 3p subshells, as well as from the 3d and 4s valence subshells.

The 4f and 5p subvalence photoionization of atomic Tm has been investigated by combining high-resolution photoelectron spectroscopy and dichroism measurements of the laser-polarized atoms. The experimental results are compared to Hartree–Fock calculations. The Tm 5p photoelectron spectrum is dominated by spin–orbit splitting whereas mixing of the final ionic states strongly influences the Tm 4f photoionization. Intermediate coupling is appropriate for the explanation of the complex Tm 4f multiplet structure, though some lines are well described within LS coupling. This suggests a partial breakdown of the LS-coupling approximation for Tm 4f photoionization. In comparison to the corresponding spectra of Eu the Tm spectra are much less affected by the admixture of 6s5d and 5d2 valence electron configurations.

The rotational structure in the vibrational transitions from ν=0 to ν=1,2,3,4 of H35Cl and H37Cl is studied in Xe, Kr and Ar matrices with high spectral resolution. A consistent set of rotational constants Bv for the vibrational levels ν=0 to 4 is derived. B0 decreases with the tightness of the cage from 9.78 cm-1 in Xe to 8.83 cm-1 in Ar for H35Cl (gas phase 10.44 cm-1). The values for B0 to B4 decrease linearly with v due to the vibration-rotation-coupling constant α which increases from 0.37 cm-1 in Xe to 0.479 cm-1 in Ar (gas 0.303) according to the cage tightness. The splitting of the R(1) transition which originates from the hindering of rotation is analyzed in Xe using the T2g-T1u and T2g-Eg transition energies. A comparison with force field calculations yields a dominant contribution of the 6th spherical harmonic YA1g6 of the octahedral matrix potential. The modulation of the potential takes a value of K6/B=17 which corresponds to a barrier for the rotation of 160 cm-1. The splitting increases with the vibrational level v which can be interpreted as a weak admixture of the YA1g4 spherical harmonic. A large isotope effect and a reduction of the T1u-A1g transition energy (R(0)-transition) beyond the crystal field value are attributed to an excentric rotation with a displacement of the center of mass of the order of 0.05 A. The vibrational energies ωe show an opposite trend with matrix atom size and decrease with polarizability from 2970 cm-1 in Ar to 2945.4 cm-1 in Xe (gas 2989.9 cm-1) while the anharmonicity ωeχe of the free molecule lies close to the Kr value and thus between that of Ar and Xe.

The 3p?3d photoionization process of atomic scandium has been studied using a configuration interaction calculation and the extended Fano formalism. The photoabsorption spectrum is influenced by strong electron-electron correlations leading to highly complex structures. Very good agreement with the experimental data is found for the lower energy region where the resonances can be assigned to 2DJ?2FJ + 1 states. For the higher energy region a reasonable description of the experimental data is found.

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.

XXX International Conference on Photonic, Electronic, and Atomic Collisions, Cairns, Australia, 25 Jul 2017 - 1 Aug 2017 ; Journal of physics / Conference Series 875, 022004(2017). doi:10.1088/1742-6596/875/3/022004, Absolute cross sections for double and triple photodetachment of O- ions have been measured at photon energies around the threshold for K-shell ionization using the photon-ion merged-beams technique at a synchrotron light-source. In addition, corresponding large-scale ab-initio calculations were carried out at a level of complexity that has never been invoked before. From the comparison between experiment and theory it becomes apparent that the inclusion of multi-electron processes such as double shake-up in the theoretical calculations is crucial for the explanation of the experimental findings., Published by IOP Publ., Bristol

Absolute cross sections for photoprocesses near the K edge of Ne+ ions and neutral Ne atoms have been determined at resolving powers up to 27000 facilitating the precise determination of natural widths of the most prominent resonances as well as the associated transition probabilities and branching ratios.

XXX International Conference on Photonic, Electronic, and Atomic Collisions, ICPEAC30, Cairns, Australia, 26 Jul 2017 - 1 Aug 2017; Journal of physics / Conference Series Conference Series 875, 112005 (2017). doi:10.1088/1742-6596/875/12/112005, First experiments along with the general capabilities of the TTXMCD endstation at P04, PETRA III, DESY are presented. The TTXMCD endstation allows measuring the magnetic properties of solids, thin films, molecules or atomic adsorbates at ultra-cold temperatures in an element specific way. At such temperatures, electron-electron interaction phenomena are studied, such as the Kondo effect for Co on Cu(100)., Published by IOP Publ., Bristol

XXX International Conference on Photonic, Electronic, and Atomic Collisions, Cairns, Australia, 25 Jul 2017 - 1 Aug 2017 ; Journal of physics / Conference Series 875, 032033(2017). doi:10.1088/1742-6596/875/4/032033, Photoionization of endohedral ${{\rm{Sc}}}_{3}{{\rm{N@C}}}_{80}^{+}$ fullerene ions is investigated using synchrotron radiation in the energy range 280 to 420 eV. In the product channels ${{\rm{Sc}}}_{3}{{\rm{N@C}}}_{80}^{2+}$ and ${{\rm{Sc}}}_{3}{{\rm{N@C}}}_{78}^{2+}$ clear signaiures of the cross section contributions arising from L-shell photoabsorption by the encapsulated Sc atoms have been detected., Published by IOP Publ., Bristol

In this work two different procedures to utilize the sol-gel technology were applied to immobilize/encapsulate enzymes and living cells. CO2 has reached levels in the atmosphere that make it a pollutant. New methods to utilize this gas to obtain products of added value can be very important, both from an environmentally point of view and from an economic standpoint. The first goal of this work was to study the first reaction of a sequential, three-step, enzymatic process that carries out the conversion of CO2 to methanol. Of the three oxidoreductases involved, our focus was on formate dehydrogenase (FateDH) that converts CO2 to formate. This reaction requires the presence of the cofactor β-nicotinamide adenine dinucleotide in reduced form (NADH). The cofactor is expensive and unstable. Our experiments were directed towards generating NADH from its oxidized form (NAD+), using glutamate dehydrogenase (GDH). The formation of NADH from NAD+ in aqueous medium was studied with both free and sol-gel entrapped GDH. This reaction was then followed by the conversion of CO2 to formate, catalysed by free or sol-gel entrapped FateDH. The quantification of NADH/NAD+ was made using UV/Vis spectroscopy. Our results showed that it was possible to couple the GDH-catalyzed generation of the cofactor NADH with the FateDH-catalyzed conversion of CO2, as confirmed by the detection of formate in the medium, using High Performance Liquid Chromatography (HPLC). The immobilization of living cells can be advantageous from the standpoint of ease of recovery, reutilization and physical separation from the medium. Also dead cells may not always exhibit enzymatic activities found with living cells. In this work cell encapsulation was performed using Escherichia coli bacteria. To reduce toxicity for living organisms, the sol-gel method was different than for enzymes, and involved the use of aqueous-based precursors. Initial encapsulation experiments and viability tests were carried out with E. coli K12. Our results showed that sol-gel entrapment of the cells was achieved, and that cell viability could be increased with additives, namely betaine that led to greater viability improvement and was selected for further studies. For an approach to “in-cell” Nuclear Magnetic Resonance (NMR) experiments, the expression of the protein ctCBM11 was performed in E. coli BL21. It was possible to obtain an NMR signal from the entrapped cells, a considerable proportion of which remained alive after the NMR experiments. However, it was not possible to obtain a distinctive NMR signal from the target protein to distinguish it from the other proteins in the cell.

Single, double, and triple ionization of C(1+) ions by single photons is investigated in the energy range of 286-326 eV, i.e., in the range from the lowest-energy K-vacancy resonances to well beyond the K-shell ionization threshold. Clear signatures of C(1+)(1s2s(2)2p(2) (2)D,(2)P) resonances are found in the triple-ionization channel. The only possible mechanism producing C(4+)(1s(2)) via these resonances is direct triple-Auger decay, i.e., a four-electron process with simultaneous emission of three electrons.

The photon-ion merged-beams technique has been employed at the new Photon-Ion spectrometer at PETRA III (PIPE) for measuring multiple photoionization of Xe$^{q+}$ (q=1-5) ions. Total ionization cross sections have been obtained on an absolute scale for the dominant ionization reactions of the type h\nu + Xe$^{q+}$ $\to$ Xe$^{r+}$ + (q-r) e$^-$ with product charge states q+2 $\le$ r $\le$ q+5. Prominent ionization features are observed in the photon-energy range 650-750 eV, which are associated with excitation or ionization of an inner-shell 3d electron. Single-configuration Dirac-Fock calculations agree quantitatively with the experimental cross sections for non-resonant photoabsorption, but fail to reproduce all details of the measured ionization resonance structures., Comment: 20 pages, 12 figures, submitted for publication to J. Phys. B

Journal of physics / Conference Series 488(14), 142006 (2014). doi:10.1088/1742-6596/488/14/142006, A photon-ion merged beam endstation has been set up at the variable polarization XUV-beamline P04 of PETRA III in Hamburg. In a commissioning experiment first results could be obtained for multiple photoionization of Xe$^{q+}$ ions (q = 1,2,..,5) at photon energies around the 3d ionization threshold., Published by IOP Publ., Bristol

The time-dependent multiphoton ionization of xenon atoms is studied with femtosecond pulses in the excitation range of the $4d$ giant resonance at the photon energy of 93 eV. Benefiting from a new operation mode of the free electron laser FLASH, the measurements are performed with varying pulse durations. A strong dependence of the ion charge distribution on the pulse duration allows the different multiphoton mechanisms behind the multiple photoionization of xenon to be disentangled up to a charge state of ${\mathrm{Xe}}^{10+}$. The results up to ${\mathrm{Xe}}^{8+}$ are well explained by sequences of single photon, multiphoton, and Auger processes, but higher charge state generation suggests the need for collective electron multiphoton excitations.

High resolution, vibrationally resolved, near-edge x-ray absorption fine structure (NEXAFS) spectra at the C 1s and N 1s ionization thresholds of pyridine and deuterated d5-pyridine in the gas phase have been recorded. The high resolution of 65 meV (150 meV) at the C s (N 1s) ionization thresholds reveals vibrational structures in the spectra. Detailed ab initio and density functional theory (DFT) calculations were performed to interpret the experimental spectra and to assign the observed peaks. In particular we focused on the previously unexplained intensity ratio for the two components of the C 1s→1π* transition. For this transition the vibrational structure is included through a linear coupling model in the DFT calculations and leads to the experimentally observed ∼2:3 intensity ratio between the two π* components in the C 1s spectrum rather than the ∼3:2 ratio obtained without vibrational effects. After inclusion of relaxation effects in the excited states, in addition to the vibrational effects, both theoretical methods yield almost perfect agreement with experiment.

The 2p resonances of atomic scandium at 391-410 eV were studied by photoion spectroscopy using monochromatized synchrotron radiation and the atomic beam technique. The partial ion yield spectra for singly to quadruply charged photoions were observed. The comparison of the total ion yield spectrum with the calculated absorption spectrum shows surprisingly good results.

The optical and mechanical design of a 10 m-normal incidence monochromator for highest resolving power in the energy range from 10 to 40 eV will be presented. In order to overcome problems associated with higher order contamination, this beamline will be installed at the quasi-periodic undulator U125-2 at BESSY II.

The photoionization spectrum of helium shows considerable complexity close to the double-ionization threshold. By analyzing the results from both our recent experiments and ab initio three- and one-dimensional calculations, we show that the statistical properties of the spacings between neighboring energy levels clearly display a transition towards quantum chaos.

The cross section for the resonant 2p photoabsorption of atomic chlorine has been calculated using the configuration-interaction method with relativistic corrections. In contrast to argon no simple Rydberg series can be found in the spectrum. This is due to the large number of resonances and the strong coupling between them. Compared with the Ar spectra very narrow linewidths are observed for some resonances below the 2p threshold. Linewidths comparable with the values of the Ar states are calculated for resonances that exhibit the same symmetry for the core electrons. Above the first ionization threshold the resonances can decay via spin-flip resulting in a larger linewidth. It is shown that this decay channel is dominant for most of the chlorine states. The results are in good agreement with recent experimental data.

Physical review / B 62(21), 14331 - 14336 (2000). doi:10.1103/PhysRevB.62.14331, Published by Inst., Woodbury, NY

The dual laser plasma photoabsorption technique has been used to measure the time-resolved vacuum-UV photoabsorption spectrum of a chromium plasma. Resonant photoabsorption cross sections, constructed with the aid of Hartree-Fock calculations, and weighted in accordance with the plasma temperature, have been used to produce the synthetic Cr2+ spectra. The relevant plasma temperature and ionization balance are obtained from simple analytical models for various times during the expansion phase of the plasma plume. The experimental spectra taken at delays of 32, 62 and 90 ns compare well with Cr2+ spectra computed for corresponding predicted temperatures. It is found that in order to produce synthetic spectra that match experiment well, it is necessary to take into account absorption from many states belonging to the Cr2+ ground state configuration 3p63d4, while states from the nearest metastable configuration 3p63p34s make a negligible contribution.

The 3p photoelectron spectrum of atomic scandium, the first 3d transition metal, has been investigated experimentally using monochromatized synchrotron radiation. The threshold energies for direct 3p photoionization have been extracted from the photoelectron spectrum. The 3p-1 multiplet structure is discussed based on the predictions of Hartree-Fock (HF) calculations and recent results from multi-configuration Hartree-Fock (MCHF) calculations by Altun and Manson (1999 Phys. Rev. A 59 3576). Due to the characteristics of the 3p-13d configuration, scandium reveals a peculiar multiplet splitting, which differs significantly from those of other 3d transition metal atoms.

Recently, the spectrum of singly ionized chromium has come under theoretical scrutiny by Dolmatov (1996 J. Phys. B: At. Mol. Opt. Phys. 29 L673) and also by Donnelly et al (1997 J. Phys. B: At. Mol. Opt. Phys. 30 L285). Both of these theoretical investigations, employing the spin-polarized RPAE (SPRPAE) and R-matrix techniques, respectively, concerned the 3p photoabsorption cross section from the 3d5 6S5/2 ground state of Cr+. The two calculations are consistent with each other and agree with the previously reported experimental data for the 3p4s resonances and the onset of the 3p3d giant resonance (Costello 1991 Phys. Rev. A 43 1441). However, beyond the peak of the giant resonance, both calculations result in cross sections which differ considerably from the experimental data. From further dual-laser plasma experiments carried out under different spatio-temporal conditions and atomic structure calculations on metastable states this discrepancy can be ascribed to the presence of metastable excited singly ionized chromium within the plasma.

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.

We present the design characteristics of an XUV undulator beamline for BESSY II, based on a spherical-grating monochromator for the energy range from 35–500 eV. The monochromator will use a moveable pre-mirror and a moveable exit slit and has been optimized for highest resolution. For photon energies up to 200 eV a resolving power of 50 000 up to 80 000 should be achievable, and for higher energies a resolving power of 20 000. All properties of the beamline have been extracted from ray-tracing calculations taking slope errors as well as the characteristics of the source into account.

The direct 5p photoionization of atomic Lu has been investigated by photoelectron spectroscopy in combination with monochromatized synchrotron radiation. Binding energies of the multiplet states have been determined from the photoelectron spectra. For the interpretation of the multiplet structure, we performed Hartree-Fock calculations, where configuration interaction was taken into account. The main result is that the splitting of the multiplet structure is dominated by the spin-orbit interaction.

The \(\) resonances of atomic Lu have been investigated by photoelectron and photoion spectroscopy using monochromatized synchrotron radiation in the vacuum ultraviolet energy region. The total photoion yield has been compared to calculations in which the extended Fano theory (Mies formalism) and the Hartree-Fock method were applied. The resonance structure is dominated by the spin-orbit splitting of the 5p core hole. In the photoion yield spectra of singly and doubly charged ions a high fraction of Lu2+ ions has been found in the region of the 5p-1(2P1/2)nd resonances. Photoelectron spectra, recorded in this resonance region, have been investigated with respect to deexcitation channels connected with Lu2+ ions. The 5p-1(2P1/2)nd resonances predominantly autoionize by spin-flip into \(\) states, which decay in the second step into Lu2+ final ionic states.

The photoionization of atomic bismuth in the complex autoionization region above the first ionization threshold Bi+ (6s(2)6p(2))P-3(0) is studied using spin-resolved photoelectron spectroscopy and Hartree-Fock calculations with relativistic extensions. In spin- and angle-resolved measurements with circularly polarized synchrotron radiation the relative photoelectron intensity and the polarization parameters A and xi are determined for the strongest resonances. In calculations taking more than 30 different configurations into account all five dynamical photoionization parameters are determined. The agreement with the experimental data is fairly good. Combining calculated and experimental results for the intensity spectrum and the polarization parameter A as well as earlier absorption data, assignments of the first autoionization resonances above the threshold are obtained leading partially to a revision of previous results.

The 3p photoelectron spectra of atomic Fe and Cu, and the Fe outer-shell satellites have been investigated. The complex multiline structure of the Fe spectra has been resolved using high-resolution electron spectroscopy. The thresholds of the direct 3p photoionization have been determined and are compared with experimental results from photoabsorption measurements and Auger spectra, and with the multiplet structures calculated taking into account intershell and configuration interaction. The stepwise decay of highly excited Fe states into has been verified by the detection of satellite lines with binding energies above the lowest ionization threshold.

The results of recent VUV photoionization experiments of the 5d elements Ta, W, Re, Ir and Pt using atomic beam technique, excitation with monochromatized synchrotron radiation and detection of singly and doubly charged photoions are discussed. Special attention is given to the resonances caused by discrete transitions of the 5p and 4f electrons into the unfilled 5d subshells. As there is a crossover of the 5p and 4f levels along the series of the 5d elements the result is a complicated structure of the corresponding interacting resonances. The photoion spectra are compared with theoretical calculations carried out within the relativistic time dependent local density and the relativistic Hartree-Fock approximation.

The ion-counting rate was investigated in a photoionization experiment using polarized and aligned oxygen atoms and linearly polarized light. The cross section of the valence photoionization was found to depend on the angle between the polarization axis of the ionizing synchrotron radiation and the axis of atomic alignment. A significant asymmetry in the ion rates corresponding to and was observed close to the resonance. This asymmetry is caused by j-dependent resonant behaviour of the and continuum channels.