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Multiple ionization of the ${\mathrm{Ar}}^{+}(3{s}^{2}3{p}^{5})$ ion by a single photon has been investigated in the photon-energy range 250--1800 eV employing the photon-ion merged-beams technique. Absolute partial cross sections were measured for all ${\mathrm{Ar}}^{(1+m)+}$ product-ion channels with $1\ensuremath{\le}m\ensuremath{\le}6$ covering a size range from several tens of Mb down to a few b. Narrow $2p$-subshell excitation resonances were observed in all channels up to quadruple ionization at a photon-energy bandwidth of 52 meV. Double excitations involving a $2p$ and a $3s$ or $3p$ electron were also studied at high resolution and the measurements of the broad $2s$ excitation resonances directly showed their natural widths. Contributions of direct photo double ionization (PDI) to the production of the highest final Ar ion charge states are revealed, with PDI of the $2s$ subshell being mainly responsible for the production of ${\mathrm{Ar}}^{7+}$. The experiment made use of the PIPE setup installed at beamline P04 of the PETRA III synchrotron light source of DESY in Hamburg. The measurements were supported by theoretical calculations to identify the main contributions to the observed cross sections. Comparisons of theory and experiment show remarkable agreement but also hint to additional ionization mechanisms that are not considered in the theoretical models such as core ionization accompanied by excitations with subsequent Auger decays leading to net $m$-fold ionization with $m\ensuremath{\ge}4$.

Recently, we have demonstrated (Jin et al. 2020, J. Phys. B: At. Mol. Opt. Phys. 53, 075201) that a hybrid subconfiguration-average and level-to-level distorted wave treatment of electron-impact single ionisation (EISI) of W$^{14+}$ ions represents an accurate and manageable approach for the calculation of EISI cross sections of a complex ion. Here we demonstrate the more general validity of this approach by comparing hybrid cross sections for EISI of W$^{15+}$ and W$^{16+}$ with the recent experimental results of Schury et al. 2020, J. Phys. B: At. Mol. Opt. Phys. 53, 015201). Our calculations also account for the resonant-excitation double autoionisation (REDA) process which is important in the electron energy range 370-600 eV and for the possible presence of initially metastable ions in the experiment., 7 pages, 8 figures, 1 table

Physical review letters 124, 083203 (2020). doi:10.1103/PhysRevLett.124.083203, We report on new measurements of m-fold photodetachment (m = 2 − 5) of carbon anions via K-shellexcitation and ionization. The experiments were carried out employing the photon-ion merged-beamstechnique at a synchrotron light source. While previous measurements were restricted to doubledetachment (m = 2) and to just the lowest-energy K-shell resonance at about 282 eV, our absoluteexperimental m-fold detachment cross sections at photon energies of up to 1000 eV exhibit a wealth of newthresholds and resonances. We tentatively identify these features with the aid of detailed atomic-structurecalculations. In particular, we find unambiguous evidence for fivefold detachment via double K-holeproduction., Published by APS, College Park, Md.

Journal of physics / Conference series 1412, 152009 (2020). doi:10.1088/1742-6596/1412/15/152009, Published by IOP Publ., Bristol

The sensitivity of an electron–ion crossed-beams experiment is mainly determined by the densities of both beams in the interaction region. Aiming at the extension of the available range of accessible electron energies and densities, a new high-power electron gun has been developed and fabricated. It delivers a ribbon-shaped beam with currents of up to 1 A at variable energies reaching 3500 eV at the maximum. The design goals of the gun are being met by using a configuration of electrodes, which allows for a variety of operation modes. Here, we report on the results of the ongoing tests of the new electron gun. In particular, electron-impact ionization cross sections of He+ and Xe5+ ions were measured employing the animated crossed-beams technique. The results are in excellent agreement with literature data.

We investigate electron-impact single ionization of He-like ions of charge state $q=0,\ensuremath{\cdots},6$ in the initial ground ($1\phantom{\rule{0.16em}{0ex}}^{1}S$) and metastable ($2\phantom{\rule{0.16em}{0ex}}^{3}S$) states. Good agreement between theory and experiment is established for the total cross sections, and then the scaling behavior with $q$ is considered as a function of the ratio $u={E}_{i}/{E}_{I}\ensuremath{\le}10$ of the incident electron energy ${E}_{i}$ and the ionization threshold ${E}_{I}$. While the expected ${E}_{I}^{2}$ scaling of the cross sections is confirmed, we also find that at each scaled energy $u$ the spin asymmetry (for the $2\phantom{\rule{0.16em}{0ex}}^{3}S$ state) converges rapidly to a nonzero constant with increasing $q$. This indicates that, despite ${E}_{I}$ increasing with ${q}^{2}$, exchange effects remain undiminished on the broad scaled-energy range considered. We suggest that this physical behavior is more universal than just for the He-like ions.

Author(s): Muller, A; Martins, M; Kilcoyne, ALD; Phaneuf, RA; Hellhund, J; Borovik, A; Holste, K; Bari, S; Buhr, T; Klumpp, S; Perry-Sassmannshausen, A; Reinwardt, S; Ricz, S; Schubert, K; Schippers, S | Abstract: Photoprocesses of the endohedral fullerene ions Sc3N@C80+ and Sc3N@C80- in the gas phase have been investigated in the photon energy ranges 30-50 eV and 280-420 eV. Single and double ionization as well as single ionization accompanied by the release of a C2 dimer were observed as a function of the photon energy for the positive parent ion and double detachment was measured for the negative parent ion. The emphasis of the experiments was on the specific effects of the encapsulated trimetallic nitride cluster Sc3N on the observed reactions. Clear evidence of photoexcitation near the Sc L edge is obtained with the dominating contributions visible in the one- and two-electron-removal channels. K-vacancy production in the encapsulated central nitrogen atom is seen in the single ionization of Sc3N@C80+ but is much less pronounced in the photoionization-with-fragmentation channel. Comparison of the cross sections near the carbon K edge with the corresponding channels measured previously in the photoionization of Lu3N@C80+ reveal strong similarities. Previously predicted sharp resonance features in the ionization of Sc3N@C80+ ions below the Sc M edge are not confirmed. The experiments are accompanied by quantum-chemistry calculations in the Hartree-Fock approximation and by model calculations employing density functional theory (DFT).

The cross section for electron-impact single ionisation of W14+ ions has been calculated by using two different approaches, i.e., the subconfiguration averaged distorted-wave (SCADW) method and the more involved level-to-level distorted-wave (LLDW) method. Both methods are found to yield very similar results except for the 4d->5d excitation-autoionisation (EA) channels that straddles the ionisation threshold. Accordingly, a hybrid theoretical cross section where the $4d\to 5d$ EA SCADW cross section is replaced by its LLDW counterpart is in good agreement with the experimental result from an electron-ion crossed-beams experiment. This is in contrast to pure SCADW calculations for W14+ and neighbouring charge states which exhibit significant deviations from the experimental near-threshold cross sections of Schury et al. [J. Phys. B 53 (2020) 015201]., 8 pages, 7 figures, 3 tables

Synopsis A detector setup for registering ion species between the poles of a dipole magnet at CRYRING@ESR has been developed. It is based on a scintillator delivering light via a quartz light guide onto a semiconductor photomultiplier. The detector is capable of operating in a strong magnetic field. It can be swiftly retracted from the exposition area during the beam injection into the ring and repositioned back for the measurement cycle to avoid unnecessary exposition and, thus, to increase the scintillator life time.

Synopsis Photoprocesses of the endohedral fullerene ions Sc 3 N @ C 80 + and Sc 3 N @ C 80 − in the gas phase have been experimentally investigated with emphasis on the specific effects of the encapsulated trimetallic nitride cluster Sc3N on the observed reaction yields. Clear evidence of photoexcitation near the Sc L edge is obtained with the dominating contributions visible in the one- and two-electron-removal channels. The experiments are accompanied by model calculations employing density functional theory (DFT).

Author(s): Muller, A; Lindroth, E; Bari, S; Borovik, A; Hillenbrand, PM; Holste, K; Indelicato, P; Kilcoyne, ALD; Klumpp, S; Martins, M; Viefhaus, J; Wilhelm, P; Schippers, S | Abstract: In a joint experimental and theoretical endeavor, photoionization of metastable C4+(1s2sS13) ions via intermediate levels with hollow, double-K-vacancy configurations 2s2p, 2s3p, 2p3s, 2p3d, 2s4p, 2p4s, and 2p4d has been investigated. High-resolution photon-ion merged-beams measurements were carried out with the resolving power reaching up to 25 800 which is sufficient to separate the leading fine-structure components of the 2s2pP3 term. Many-body perturbation theory was employed to determine level-to-level cross sections for K-shell excitation with subsequent autoionization. The resonance energies were calculated with inclusion of electron correlation and radiative contributions. Their uncertainties are estimated to be below ±1 meV. Detailed balance confirms the present photoionization cross-section results by comparison with previous dielectronic-recombination measurements. The high accuracy of the theoretical transition energies together with the present experimental results qualify photoabsorption resonances in heliumlike ions as new, greatly improved energy-reference standards at synchrotron radiation facilities.

Double and triple detachment of the ${\mathrm{F}}^{\ensuremath{-}}(1{s}^{2}2{s}^{2}2{p}^{6})$ negative ion by a single photon have been investigated in the photon energy range 660 to 1000 eV. The experimental data provide unambiguous evidence for the dominant role of direct photodouble detachment with a subsequent single-Auger process in the reaction channel leading to ${\mathrm{F}}^{2+}$ product ions. Absolute cross sections were determined for the direct removal of a $(1s+2p)$ pair of electrons from ${\mathrm{F}}^{\ensuremath{-}}$ by the absorption of a single photon.

Author(s): Muller, A; Borovik, A; Buhr, T; Hellhund, J; Holste, K; Kilcoyne, ALD; Klumpp, S; Martins, M; Ricz, S; Viefhaus, J; Schippers, S | Abstract: Single, double, and triple ionization of the C+ ion by a single photon have been investigated in the energy range 286 to 326 eV around the K-shell single-ionization threshold at an unprecedented level of detail. At energy resolutions as low as 12 meV, corresponding to a resolving power of 24 000, natural linewidths of the most prominent resonances could be determined. From the measurement of absolute cross sections, oscillator strengths, Einstein coefficients, multielectron Auger decay rates, and other transition parameters of the main K-shell excitation and decay processes are derived. The cross sections are compared to results of previous theoretical calculations. Mixed levels of agreement are found despite the relatively simple atomic structure of the C+ ion with only five electrons. This paper is a followup to a previous Letter [A. Muller, Phys. Rev. Lett. 114, 013002 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.013002].

The Photon-Ion Spectrometer at PETRA III - in short, PIPE - is a permanently installed user facility at the "Variable Polarization XUV Beamline" P04 of the synchrotron light source PETRA III operated by DESY in Hamburg, Germany. The careful design of the PIPE ion-optics in combination with the record-high photon flux at P04 has lead to a breakthrough in experimental studies of photon interactions with ionized small quantum systems. This short review provides an overview over the published scientific results from photon-ion merged-beams experiments at PIPE that were obtained since the start of P04 operations in 2013. The topics covered comprise photoionization of ions of astrophysical relevance, quantitative studies of multi-electron processes upon inner-shell photoexcitation and photoionization of negative and positive atomic ions, precision spectroscopy of photoionization resonances, photoionization and photofragmentation of molecular ions and of endohedral fullerene ions., Comment: 10 pages, 9 figures

30th International Conference on Photonic, Electronic and Atomic Collisions, ICPEAC XXX, Cairns, Australia, 26 Jul 2017 - 1 Aug 2017; Journal of physics / Conference Series 875, 052040 (2017). doi:10.1088/1742-6596/875/6/052040, A transverse free-electron target for crossed-beams collision studies is currently being developed. The target will be installed in the main experimental section of the FAIR storage ring CRYRING@ESR. The setup will allow for electron-ion collision studies with highly charged ions on an unprecedented level of detail that comprises, e.g., the angle-differential observation of photon emission., Published by IOP Publ., Bristol

The astrophysical journal 836(2), 166 (2017). doi:10.3847/1538-4357/836/2/166, Single, double, and triple photoionization of Ne$^{+}$ ions by single photons have been investigated at the synchrotron radiation source PETRA III in Hamburg, Germany. Absolute cross-sections were measured by employing the photon–ion merged-beams technique. Photon energies were between about 840 and 930 eV, covering the range from the lowest-energy resonances associated with the excitation of one single K-shell electron up to double excitations involving one K- and one L-shell electron, well beyond the K-shell ionization threshold. Also, photoionization of neutral Ne was investigated just below the K edge. The chosen photon energy bandwidths were between 32 and 500 meV, facilitating the determination of natural line widths. The uncertainty of the energy scale is estimated to be 0.2 eV. For comparison with existing theoretical calculations, astrophysically relevant photoabsorption cross-sections were inferred by summing the measured partial ionization channels. Discussion of the observed resonances in the different final ionization channels reveals the presence of complex Auger-decay mechanisms. The ejection of three electrons from the lowest K-shell-excited Ne$^{+}$$(1s 2s^{2}$ $2p^{6}$ $^{2}$$S_{1/2})$ level, for example, requires cooperative interaction of at least four electrons.

XXX International Conference on Photonic, Electronic, and Atomic Collisions, Cairns, Australia, 25 Jul 2017 - 1 Aug 2017 ; Journal of physics / Conference Series 875, 032034(2017). doi:10.1088/1742-6596/875/4/032034, Cross sections for photoionization and photofragmentation of singly, doubly and triply charged Lu3N@C80 ions have been measured using the photon-ion merged-beams technique at the PETRA III synchrotron light source. The measured spectra exhibit prominent resonance features at energies around the carbon K edge. In contrast to that, no signatures of the nitogen K and lutetium M edges have been found in the experimentally investigated reaction channels., Published by IOP Publ., Bristol

Absolute cross sections for electron-impact single ionisation (EISI) of multiply charged tungsten ions (Wq+) with charge states in the range 11 ≤ q ≤ 18 in the electron-ion collision energy ranges from below the respective ionisation thresholds up to 1000 eV were measured employing the electron-ion crossed-beams method. In order to extend the results to higher energies cross section calculations were performed using the subconfiguration-averaged distorted-wave (SCADW) method for electron-ion collision energies up to 150~keV. From the combined experimental and scaled theoretical cross sections rate coefficients were derived which are compared with the ones contained in the ADAS database and which are based on the configuration-averaged distorted wave (CADW) calculations of Loch et al. [Phys. Rev. A 72, 052716 (2005)]. Significant discrepancies were found at the temperatures where the ions investigated here are expected to form in collisionally ionised plasmas. These discrepancies are attributed to the limitations of the CADW approach and also the more detailed SCADW treatment which do not allow for a sufficiently accurate description of the EISI cross sections particularly at the ionisation thresholds.

Motivated by possible atomic origins of the unidentified emission line detected at 3.55 keV to 3.57 keV in a stacked spectrum of galaxy clusters (Bulbul et al. 2014), an electron beam ion trap (EBIT) was used to investigate the resonant dielectronic recombination (DR) process in highly-charged argon ions as a possible contributor to the emission feature. The He-like Ar DR-induced transition 1s$^2$2l - 1s2l3l$^\prime$ was suggested to produce a 3.62 keV photon (Bulbul et al. 2014) near the unidentified line at 3.57 keV and was the starting point of our investigation. The collisional-radiative model NOMAD was used to create synthetic spectra for comparison with both our EBIT measurements and with spectra produced with the AtomDB database/Astrophysical Plasma Emission Code (APEC) used in the Bulbul et al. (2014) work. Excellent agreement was found between the NOMAD and EBIT spectra, providing a high level of confidence in the atomic data used. Comparison of the NOMAD and APEC spectra revealed a number of missing features in the AtomDB database near the unidentified line. At an electron temperature of $T_e$ = 1.72 keV, the inclusion of the missing lines in AtomDB increases the total flux in the 3.5 keV to 3.66 keV energy band by a factor of 2. While important, this extra emission is not enough to explain the unidentified line found in the galaxy cluster spectra.

Electron-impact single ionization of $\mathrm{W}^{19+}$ ions has been studied both experimentally and theoretically. By employing the crossed-beams method, absolute cross sections have been measured in the energy range from the ionization onset up to 1000 eV. Theoretical calculations of the ionization-cross-section function were performed using the configuration-averaged distorted-wave method for electron-ion collision energies up to 150 keV. Contributions of excited long-lived primary-ion-beam admixtures were taken into account. The role of different competing ionization mechanisms contributing to the studied cross section is discussed. Plasma rate coefficients have been inferred and are presented in parametrized form.

We study the energy dependences of electron excitation cross sections of the autoionizing levels (5p56s2)2P3/2 and (5p55d(3P)6s)2P3/2, as well as the autoionization cross sections of cesium atoms in the impact energy range from the excitation threshold to 600 eV. It is established that an increase in the excitation cross section of the 2P3/2 levels (to 60% of the maximum value) and the deep minimum in the autoionization cross section observed in the energy region of 17–27 eV are caused by the predominance of the radiative decay channel for autoionizing levels with excitation thresholds above 17 eV. The high efficiency of the process is mainly related to the resonance excitation of these levels in the near-threshold energy region.

We measure the full autoionization cross section of lithium atoms excited by electrons in the energy range from the first autoionization threshold at 56.39 to 600 eV. Data are obtained by determining the total intensity of electron spectrum of autoionization states 1sn 1 l 1 n 2 l 2 detected at the “magic” observation angle of 54.7°. The cross section behavior is characterized by a sharp increase to a maximum value of 1.7 × 10−18 cm2 in the energy interval of 56.4–60 eV and a subsequent monotonic drop to a value of 10−18 cm2 at 600 eV. We have discovered a “thin” cross section structure that reflects the presence of strong resonances of Li− ions in the near-threshold area of excitation of the lowest energy autoionization states (1s2s2)2S, (1s2s2p)4 P, 1s(2s2p 3 P)2 P), and 1s(2s2p 1 P)2 P. We have established that the contribution of autoionization to the absolute cross section of single ionization of lithium atoms does not exceed 4%. We perform a comparative analysis of the data with analogous data for potassium and cesium atoms.

The electron excitation function for the lowest (3p 53d4s)4 P autoionizing quartet level of the potassium atom is measured in the energy range from the threshold of the process to 102 eV at the energy resolution of 0.3 eV or better. The near-threshold energy region is studied in detail for the first time. The main processes that govern the dynamics of excitation of the low-lying quartet levels in the potassium atom are analyzed by comparing these data with the excitation functions obtained earlier for the (3p 54s4p)4 S and (3p 54s4p)4 D levels. In particular, the resonances of negative ions in the near-threshold energy region are shown to play a dominant role, as well as to significantly affect the efficiency of the cascade transitions from higher-lying quartet levels.

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.

Technological requirements analyzed to the electric drive of pulling device for horizontal continuous casting machine with billets type of circular cross section. Modular construction system of the electric pulling device considered as a way to expand the range of produced at the facility cross sections and product mix.

The ejected-electron spectra arising from the decay of the 5p5n1l1n2l2n3l3 autoionizing states in Ba atoms were precisely measured for electron impact energies between 15 and 20 eV. The excitation threshold of the 5p6 subshell was evaluated at 15.63 ±0.05 eV. The excitation thresholds and decay paths of the lowest states in 5p55d6s2 and 5p55d26s configurations were determined.

The cascade population of the (3p54s2)2P3/2, 1/2 lowest autoionizing levels in potassium has been studied to shed light on recent experimental observations of a noticeable enhancement in the cross sections around 22 eV incident electron energy. The ejected-electron excitation functions of both levels have been re-measured in the range of 20–28 eV, and calculations of the decay parameters for the 3p54s4p levels have been performed in single-configuration Hartree–Fock and configuration-interaction approaches. The analysis of these results, together with other available experimental and theoretical data on the 3p subshell excitation in potassium, revealed a relatively small contribution (

Ejected-electron excitation functions for the lowest-lying (3p54s2)2P3/2 and (3p54s2)2P1/2 autoionizing states in potassium have been measured for incident-electron energies from threshold to 500 eV and 200 eV, respectively, with improved energy resolution. Strong resonances have been observed and well resolved in the excitation functions of both states near their excitation thresholds. R-matrix (close-coupling) calculations were performed to analyse and tentatively assign these features. A remarkable similarity between the spectrum of the core-excited negative-ion potassium states and the excited states of atomic argon is noted.

A high-power electron gun delivering a ribbon-shaped electron beam with energies of 10-3500 eV and high currents at all energies is currently being commissioned at the electron-ion crossed-beams setup in Giessen. As compared to the formerly used electron gun [1], the new one will enable us to perform measurements of cross-sections for electron-impact ionization of ions in a wider energy range and, consequently, for ion charge states that were not accessible before.

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.

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 role of hollow states intermediately produced in electron-impact ionization of metastable He-like $N{}^{5+}(1s2s{\phantom{\rule{0.16em}{0ex}}}^{3}{S}_{1})$ ions has been investigated in detail. A crossed-beam setup and suitable experimental techniques were employed for the measurement of accurate absolute cross sections and precise energy-scan data. Fine structures arising from $K$-shell excitations and associated resonances have been observed for this two-electron ion with less than $\ifmmode\pm\else\textpm\fi{}$0.5 eV uncertainty on the energy scale. Fine details, such as interference of the reaction pathways of direct ionization and excitation with capture of the incident electron followed by double-Auger decay, could be revealed. Ab initio calculations based on the convergent close coupling (CCC) approach are in good agreement with the experiment.

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

Single ionization of noble-gas atoms by linearly polarized synchrotron radiation has been studied by employing angle- and energy-resolved photoelectron spectroscopy. The measurements were carried out in the plane defined by the momentum and polarization vectors of the photon. Parameters describing the left-right asymmetry (LRA; relative to the photon propagation direction) of the photoelectron angular distribution were determined experimentally for the $s$ shells of He, Ne, Ar, Kr, and Xe atoms and $\mathrm{H}{}_{2}$ molecules and for the $p$ shells of Ne, Ar, Kr, and Xe atoms. The values of the left-right asymmetry differ significantly from zero for both subshells. The photon and photoelectron energy dependence of the LRA parameters is presented also. Possible experimental and instrumental sources that could generate asymmetry are discussed and excluded as well.

The excitation-autoionization cross section of sodium atoms was studied as a function of the incident electron energy over the range from the lowest autoionization threshold at 30.77 eV up to 400 eV. The present data are compared with the similar excitation-autoionization cross sections for Li, K, Rb, and Cs atoms.

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

A surface detector for the detection of metal atoms in metastable states is described. The surface used for de-excitation of the metastable atoms is produced from the condensed vapour of the target metal. The resulting secondary-electron emission is detected by a channel electron multiplier. The design offers the important advantage of a low work function and high selectivity for the secondary electrons. Efficient cooling of the detection surface and the electron multiplier makes it possible to use the detector in studies of metal vapours at temperatures of up to 400 °C. An example of the use of the detector to measure the electron-impact excitation function for inner-shell excited metastable states in potassium is presented.

We have measured the energy dependences that govern the cross sections for Minsk, electron-impact excitation of spectral transitions from the levels of alkali-earth atoms that correspond to a simultaneous excitation of s 2-valent electrons. Measurements were performed on a setup with intersecting beams of atoms and electrons. The energy dependences for two- and one-electron excitations are compared. It is found that the energy dependences for the spectral transitions from one- and two-electron excitation levels that have the same orbital quantum numbers are similar.

The metastable excitation function and the near-threshold energy loss spectrum in potassium, corresponding to 3p6 core excitation, have been measured over the energy range 18-24 eV. Many structures have been observed for the first time in the metastable excitation function. From a comparison of the observed yields of metastable atoms and scattered electrons, various processes for metastable production are considered, including resonance excitation and radiative cascade. The excitation thresholds for the lowest-lying metastable autoionizing levels in potassium, namely 3p54s4p 4D7/2 and 3p53d4s 4F9/2, have been determined to be 20.28±0.05 eV and 20.42±0.05 eV, respectively.

The ejected-electron excitation functions of the lowest-lying autoionizing states (1s2s2) 2S, (1s2s2p) 4P1/2,3/2, 1s(2s2p 3P) 2P and 1s(2s2p 1P) 2P in lithium atoms have been measured for the first time at the magic angle of 54.7°. The measurements have been performed at the energy resolution of 0.4 eV over the electron impact energy range from the excitation thresholds up to 600 eV. In all excitation functions the strong resonance structures are revealed just above the excitation thresholds and in the high-impact energy region. The near-threshold structures are tentatively assigned to the shape resonances and autodetaching states of the lowest-lying 1s2s2p2, 1s2s2p3s, 1s2s2p3p and 1s2p3 Li- configurations. Above 61 eV the radiative cascade transitions from the upper autoionizing levels are considered to interpret the data. The results obtained point out the important role of negative-ion resonances in the near-threshold excitation of autoionizing states in lithium atoms.

The ejected-electron spectra corresponding to the radiationless decay of 5p5 states in Ba atoms have been measured precisely for different incident electron energies ranging from the appearance of the first autoionizing line at 15.68 eV up to 140 eV. The spectra have been obtained at an observation angle of 54.7? and with incident-electron and ejected-electron energy resolutions of 0.2 eV and 0.07 eV, respectively. In total, 63 lines with excitation thresholds below 22 eV have been observed between 9.8 and 16.6 eV ejected-electron kinetic energy. Based on measured excitation energies, intensity behavior of lines, calculated excitation energies, cross sections and decay rates of states in 5p56s, 5p55d and 5p55d6snl configurations, assignments for all 63 lines are proposed. The excitation and decay processes for classified autoionizing states have been examined and compared with existing data. The excitation threshold of the subshell has been established at 15.61 ? 0.05 eV.

The angular distribution of the Kr $4p$ photoelectrons was investigated in the photon energy range of the $(3d){}^{\ensuremath{-}1}\ensuremath{\rightarrow}\mathit{np}$ resonant excitations. The experimental dipole ($\ensuremath{\beta}$) and nondipole ($\ensuremath{\gamma}$ and $\ensuremath{\delta}$) anisotropy parameters were determined for the spin-orbit components of the Kr $4p$ shell. A simple theoretical model was developed for the description of the photoionization and excitation processes. An interference effect was observed between the direct photoionization and the resonant excitation participator Auger decay processes in the photon energy dependence of the experimental anisotropy parameters.

The ionization of Mg 2p by electron impact has been studied at about 400 and 1000 eV incident energy and small momentum transfer via (e,2e) experiments. Two kinematical conditions have been chosen in order to study the coincidence angular distribution in the case where either only the direct 2p ionization contributes or the decay of the 2p core hole plays a role, too. The results have been compared with distorted-wave Born approximation calculations.

Relative cross sections for photoionization and photofragmentation of endohedral fullerene Lu3N@C80q+ (q=1,2,3) ions have been measured employing the new photon-ion spectrometer PIPE at PETRA III. Prominent structures related to the carbon K-shell ionization threshold were observed in the energy range 280 to 330 eV.

An extremely efficient method for the production of highly charged ions has been realized. The method is based on the control of a local ion trap created by the rippled electron beam in a focusing magnetic field. Highly charged ions such as, for example, neon-like iridium can be prepared in the room-temperature hand-size device. This offers wide opportunities for laboratory studies of a variety of physical problems.