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Physical chemistry, chemical physics 24(38), 23119 - 23127 (2022). doi:10.1039/D2CP02383K special issue: "Ions, electrons, coincidences and dynamics: Festschrift for John H.D. Eland", We report the X-ray absorption of isolated H3O+ cations at the O 1s edge. The molecular ions were prepared in a flowing afterglow ion source which was designed for the production of small water clusters, protonated water clusters, and hydrated ions. Isolated H2O+ cations have been analyzed for comparison. The spectra show significant differences in resonance energies and widths compared to neutral H2O with resonances shifting to higher energies by as much as 10 eV and resonance widths increasing by as much as a factor of 5. The experimental results are supported by time-dependent density functional theory calculations performed for both molecular cations, showing a good agreement with the experimental data. The spectra reported here could enable the identification of the individual molecules in charged small water clusters or liquid water using X-ray absorption spectroscopy., Published by RSC Publ., Cambridge

The F 1s core level photoionization of the ionic molecular radical HF+ has been studied using the photon-ion merged-beams technique at a synchrotron radiation source. Upon analyzing kinetic energy release (KER) dependent photoion yield spectra, complex ultrafast dissociation dynamics of the F 1s core hole excited σ* state can be revealed. By means of configuration-interaction electronic structure calculations of the excited molecular potential energy curves, this complex process can be attributed to a spin-dependent dissociation of the excited σ* biradical state.

Observations of CH$^+$ are used to trace the physical properties of diffuse clouds, but this requires an accurate understanding of the underlying CH$^+$ chemistry. Until this work, the most uncertain reaction in that chemistry was dissociative recombination (DR) of CH$^+$. Using an electron-ion merged-beams experiment at the Cryogenic Storage Ring, we have determined the DR rate coefficient of the CH$^+$ electronic, vibrational, and rotational ground state applicable for different diffuse cloud conditions. Our results reduce the previously unrecognized order-of-magnitude uncertainty in the CH$^+$ DR rate coefficient to $\sim \pm 20\%$ and are applicable at all temperatures relevant to diffuse clouds, ranging from quiescent gas to gas locally heated by processes such as shocks and turbulence. Based on a simple chemical network, we find that DR can be an important destruction mechanism at temperatures relevant to quiescent gas. As the temperature increases locally, DR can continue to be important up to temperatures of $ \sim 600\,\mathrm{K} $ if there is also a corresponding increase in the electron fraction of the gas. Our new CH$^+$ DR rate coefficient data will increase the reliability of future studies of diffuse cloud physical properties via CH$^+$ abundance observations., Comment: Main paper: PDFLaTeX with 7 pages, 3 figures. Appendix starting on page 7: PDFLaTeX with 11 pages, 2 figures, 4 tables. This article has been accepted by The Astrophysical Journal

Physical review / A 104(5), 053107 (2021). doi:10.1103/PhysRevA.104.053107, Experimental cross sections for $m$-fold photodetachment ($m=3-6$) of silicon anions via $K$-shell excitation and ionization were measured in the photon-energy range of 1830-1900~eV using the photon-ion merged-beams technique at a synchrotron light source. All cross sections exhibit a threshold behavior that is masked by pre-threshold resonances associated with the excitation of a $1s$ electron to higher, either partly occupied or unoccupied atomic subshells. Results from multi-configuration Dirac-Fock (MCDF) calculations agree with the experimentally derived cross sections for photo-absorption if small energy shifts are applied to the calculated resonance positions and detachment thresholds. Moreover, a systematic approach is applied for modeling the deexcitation cascades that set in after the initial creation of a $K$-shell hole. The resulting product charge-state distributions compare well with the measured ones for direct $K$-shell detachment but less well for resonant $K$-shell excitation. The present results are potentially useful for identifying silicon anions in cold plasmas such as interstellar gas clouds., Published by Inst., Woodbury, NY

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 $m\ensuremath{\ge}4$.

Author(s): Muller, A; Kilcoyne, ALD; Phaneuf, RA; Holste, K; Schippers, S; Kheifets, AS | Abstract: Direct double ionization of the Ar+(3p-1) ion by a single photon is investigated both experimentally and theoretically. The photon-ion merged-beams technique was employed at the Advanced Light Source in Berkeley, USA, to measure absolute cross sections in the energy range from 60 to 150 eV. In this range, three contributions to the double ionization of Ar+ are to be expected: the removal of two 3p electrons, of a 3s and a 3p electron, and of two 3s electrons. Among the possible mechanisms leading to double ionization, the TS1 (two-step one) process dominates in the near-threshold region. In TS1, a photoelectron is ejected and, on its way out, knocks out a secondary electron. This two-step mechanism is treated theoretically by multiplying the calculated cross section for direct single photoionization of a given subshell with the calculated (e,2e) ionization probability for the ejected photoelectron to knock off a secondary electron. The calculated cross section is in very good agreement with the experiment.

The astrophysical journal 908(1), 52 - (2021). doi:10.3847/1538-4357/abcc64, Using the photon-ion merged-beams technique at a synchrotron light source, we have measured relative cross sections for single and up to five-fold photoionization of Fe$^{2+}$ ions in the energy range 690--920~eV. This range contains thresholds and resonances associated with ionization and excitation of $2p$ and $2s$ electrons. Calculations were performed to simulate the total absorption spectra. The theoretical results show very good agreement with the experimental data, if overall energy shifts of up to 2.5~eV are applied to the calculated resonance positions and assumptions are made about the initial experimental population of the various levels of the Fe$^{2+}$([Ar]$3d^6$) ground configuration. Furthermore, we performed extensive calculations of the Auger cascades that result when an electron is removed from the $2p$ subshell of Fe$^{2+}$. These computations lead to a better agreement with the measured product-charge-state distributions as compared to earlier work. We conclude that the $L$-shell absorption features of low-charged iron ions are useful for identifying gas-phase iron in the interstellar medium and for discriminating against the various forms of condensed-phase iron bound to composite interstellar dust grains., Published by Univ.11032, Chicago, Ill. [u.a.]

International audience; The transition from old space to new space along with increasing commercialization has a major impact on space flight, in general, and on electric propulsion (EP) by ion thrusters, in particular. Ion thrusters are nowadays used as primary propulsion systems in space. This article describes how these changes related to new space affect various aspects that are important for the development of EP systems. Starting with a historical overview of the development of space flight and of the technology of EP systems, a number of important missions with EP and the underlying technologies are presented. The focus of our discussion is the technology of the radio frequency ion thruster as a prominent member of the gridded ion engine family. Based on this discussion, we give an overview of important research topics such as the search for alternative propellants, the development of reliable neutralizer concepts based on novel insert materials, as well as promising neutralizer-free propulsion concepts. In addition, aspects of thruster modeling and requirements for test facilities are discussed. Furthermore, we address aspects of space electronics with regard to the development of highly efficient electronic components as well as aspects of electromagnetic compatibility and radiation hardness. This article concludes with a presentation of the interaction of EP systems with the spacecraft.

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

Journal of physics / B Atomic, molecular and optical physics 53(19), 1-8 (2020). doi:10.1088/1361-6455/aba719 special issue: "Special issue on Frontiers of AMO Science with FELs and Synchrotron Radiation", We review the recent experimental and theoretical progress in $K$-shell detachment studies of atomic anions. On the experimental side, this field has largely benefitted from technical advances at 3rd generation synchrotron radiation sources. For multiple detachment of C$^-$, O$^-$, and F$^-$ ions, recent results were obtained at the photon-ion merged-beams setup PIPE which is a permanent end station at beamline P04 of the PETRA\,III synchrotron light source in Hamburg. In addition to a much increased photon flux as compared to what was available previously, the PIPE setup has an extraordinary detection sensitivity for heavy charged reaction products that allows one to study detachment processes with extremely low cross sections in the kilobarn range, e.g., for processes involving the simultaneous creation of two core-holes by a single photon as observed in the net triple detachment of F$^-$ and the net five-fold detachment of C$^-$. Moreover, hitherto disregarded photodetachment resonances have been discovered, which exhibit a variety of line-shapes. For O$^-$ the core-hole lifetime could be determined precisely from a high-resolution measurement of a photodetachment resonance. These experimental findings pose new challenges for state-of-the-art atomic theory and require calculations combining photoexcitation (ionization) with decay cascade processes that follow after initial core-hole production., Published by IOP Publ., Bristol

Atoms 8(3), 1-17 (2020). doi:10.3390/atoms8030045 special issue: "Interaction of Ionizing Photons with Atomic and Molecular Ions", We review recent work on the photoionization of atomic ions of astrophysical interest that has been carried out at the photon-ion merged-beams setup PIPE, a permanently installed end station at the XUV beamline P04 of the PETRA III synchrotron radiation source operated by DESY in Hamburg, Germany. Our results on single and multiple $L$-shell photoionization of Fe${^+}$, Fe$^{2+}$, and Fe$^{3+}$ ions and on single and multiple $K$-shell photoionization of C$^{-}$, C$^{+}$, C$^{4+}$, Ne$^{+}$, and Si$^{2+}$ ions are discussed in astrophysical contexts. Moreover, these experimental results bear witness of the fact, that the implementation of the photon-ion merged-beams method at one of the world's brightest synchrotron light sources has led to a breakthrough for the experimental study of atomic inner-shell photoionization processes with ions., Published by MDPI, Basel

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

Journal of physics / Conference series Conference series [...] 1412, 152024 - (2020). doi:10.1088/1742-6596/1412/15/152024, Single and multiple photoionization of Si1+, Si2+, and Si3+ ions have been investigated near thesilicon K-edge using the PIPE setup at beamline P04 of the synchrotron light source PETRA III operated byDESY in Hamburg, Germany. Pronounced resonance structures are observed for all ions which are associatedwith excitation or ionization of a K-shell electron. The experimental cross sections are compared with resultsfrom theoretical calculations., Published by IOP Publ.20382, 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.

Yields of atomic iodine I

Experimental and theoretical cross sections are reported for single-photon single ionization of W$^{5+}$ ions. Absolute measurements were conducted employing the photon-ion merged-beams technique. Detailed photon-energy scans were performed at (67$\pm$10)~meV resolution in the 20 -- 160 eV range. In contrast to photoionization of tungsten ions in lower charge states, the cross section is dominated by narrow, densely-spaced resonances. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach employing a basis set of 457 levels providing cross sections for photoionization of W$^{5+}$ ions in the $4f^{14}5s^2 5p^6 5d \; {^2}{\rm D}_{3/2}$ ground level as well as the $4f^{14}5s^2 5p^6 5d \; {^2}{\rm D}_{5/2}$ and $4f^{14}5s^2 5p^6 6s \; {^2}{\rm S}_{1/2}$ metastable excited levels. Considering the complexity of the electronic structure of tungsten ions in low charge states, the agreement between theory and experiment is satisfactory., 15 pages, 5 figures, 2 tables. Accepted for publication in J. Phys. B: At. Mol. Opt. Phys. arXiv admin note: text overlap with arXiv:1703.00892

Ion yields following X-ray absorption of the cationic series NH

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).

We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zero to relativistic speeds. Modern theoretical and experimental approaches provide detailed insight into the wide range of many-body interactions involving projectiles and targets of varying complexity ranging from simple atoms, through molecules and clusters, complex biomolecules and nanoparticles to surfaces and crystals. These developments have been driven by technological progress and future developments will expand the horizon of the systems that can be studied. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting nineteen contributions from leading scientists in the field., Journal of Physics B: Atomic, Molecular and Optical Physics, 52 (17), ISSN:1361-6455, ISSN:0368-3508, ISSN:0953-4075, ISSN:0022-3700

Our prime computational effort is to support current and future measurements of atomic photoionization cross-sections at various synchrotron radiation facilities, and ion-atom collision experiments, together with plasma, fusion and astrophysical applications. In our work we solve the Schrodinger or Dirac equation using the R-matrix or R-matrix with pseudo-states approach from first principles. Finally, we present cross-sections and rates for radiative charge transfer, radiative association, and photodissociation collision processes between atoms and ions of interest for several astrophysical applications.

The astrophysical journal / 1 Part 1 887(2), 189 - (2019). doi:10.3847/1538-4357/ab5118, Relative cross sections for m-fold photoionization (m=1,K,5) of Fe3+ by single-photon absorption weremeasured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source operatedat DESY in Hamburg, Germany. The photon energies used spanned the range of 680–950 eV, covering both thephotoexcitation resonances from the 2p and 2s shells, as well as the direct ionization from both shells.Multiconfiguration Dirac–Hartree–Fock (MCDHF) calculations were performed to simulate the totalphotoexcitation spectra. Good agreement was found with the experimental results. These computations helpedto assign several strong resonance features to specific transitions. We also carried out Hartree–Fock calculationswith relativistic extensions taking into account both photoexcitation and photoionization. Furthermore, weperformed extensive MCDHF calculations of the Auger cascades that result when an electron is removed from the2p and 2s shells of Fe3+. Our theoretically predicted charge-state fractions are in good agreement with theexperimental results, representing a substantial improvement over previous theoretical calculations. The mainreason for the disagreement with the previous calculations is their lack of inclusion of slow Auger decays of severalconfigurations that can only proceed when accompanied by de-excitation of two electrons. In such cases, thisadditional shake-down transition of a (sub)valence electron is required to gain the necessary energy for the releaseof the Auger electron., Published by Institute of Physics Publ., London

Physical chemistry, chemical physics 21(45), 25415-25424 (2019). doi:10.1039/C9CP04640B, Yields of atomic iodine Iq+ (q Z 2) fragments resulting from photoexcitation and photoionisation of thetarget cations CHxI+ (x = 0–3) have been measured in the photon-energy range 610 eV to 670 eV,which comprises the threshold for iodine 3d ionisation. The measured ion-yield spectra show twostrong and broad resonance features due to the excitation of the 3d3/2,5/2 electrons into ef states similarto atomic iodine. In the 3d pre-edge range, electrons are excited into molecular orbitals consisting ofiodine, carbon, and hydrogen atomic orbitals. These transitions have been identified by comparison withliterature data and by simulations using time-dependent density functional theory (TDDFT) with theKMLYP functional. The ion-yield spectrum for CH3I+ resembles the spectrum of IH+ [Klumpp et al., Phys.Rev. A, 2018, 97, 033401] because the highest occupied molecular orbitals (HOMO) of the H and CH3fragments both contain a single vacancy, only. For the molecular cations with higher number ofvacancies in the valence molecular orbitals CHxI+ (x = 0–2), a stronger hybridisation of the molecularorbitals occurs between the organic fragment and the iodine resulting in a change of bonding from asingle s bond in CH3I+ to a triple bond including two p orbitals in CI+. This is reflected in the resonanceenergies of the observed absorption lines below the iodine 3d excitation threshold., Published by RSC Publ., Cambridge

A brief overview on the status of experimental investigations into photoionization and fragmentation of fullerenes and endohedral fullerenes by absorption of a single short-wavelength photon is presented. The focus of this paper is on the endohedral Xe@C60 + molecular ion in which a xenon atom is centrally encapsulated inside a C 60 + fullerene cage. Confinement resonances that result from the interference of Xe photoelectron matter waves emerging from the C 60 + cavity were studied by exposing Xe@C60 + ions to synchrotron radiation of 60 to 150 eV energy which is the region of the well-known giant atomic Xe 4 d excitation resonance. Photoions Xe@C n q+ (with final charge states q = 2 , 3 , 4 of the product ions and numbers n = 60 , 58 , 56 , 54 of carbon atoms left in the cage) were recorded as a function of photon energy and cross sections for the individual reaction channels were determined. In addition to previous work, new final channels ( q = 2 ; n = 60 , 58 and q = 4 ; n = 58 , 56 ) were observed, and thus, about 70% of the oscillator strength expected for the encapsulated Xe atom in the investigated energy range could be recovered. The present results establish the first and, so far, only conclusive experimental observation of confinement resonances in an endohedral fullerene. The data are in remarkable agreement with relativistic R-matrix calculations that accompanied the previous experimental work.

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 At the main cooler storage ring (CSRm) of IMP, Lanzhou, we have measured merged-beams rate coefficients for dielectronic recombination (DR) of F-like Ni in the energy range 0-160 eV which comprises all DR resonances associated with ΔN = 0 core excitations. We compare our results with calculations by the flexible atomic code (FAC). Good agreement is found between calculated and measured resonance parameters except for the low-energy 2s 2p6 (2S1/2)61 resonances. In addition, we have also derived plasma rate-coefficients from our data for applications in astrophysics.

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).

31st International Conference on Photonic, Electronic and Atomic Collisions, ICPEAC XXXI, Deauville, France, 23 Jul 2019 - 30 Jul 2019; Journal of physics / Conference series 1412, 152072 (2020). doi:10.1088/1742-6596/1412/15/152072, Published by IOP Publ., Bristol

Seit 2008 lassen sich visionare Entwicklungen im Konigreich Saudi-Arabien identifizieren, die die Ausrichtung berufsbildender Prozesse sehr viel starker mittels marktwirtschaftlicher Mechanismen in den Blick nimmt.

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.

Electron–ion recombination of Be-like 40Ar14+ has been measured by employing the electron–ion merged-beams method at the cooler storage ring CSRm. The measured absolute recombination rate coefficients for collision energies from 0 to 60 eV are presented, covering all dielectronic recombination (DR) resonances associated with 2s 2 → 2s2p core transitions. In addition, strong trielectronic recombination (TR) resonances associated with 2s 2 → 2p 2 core transitions were observed. Both DR and TR processes lead to series of peaks in the measured recombination spectrum, which have been identified by the Rydberg formula. Theoretical calculations of recombination rate coefficients were performed using the state-of-the-art multi-configuration Breit–Pauli atomic structure code AUTOSTRUCTURE to compare with the experimental results. The plasma rate coefficients for DR+TR of Ar14+ were deduced from the measured electron–ion recombination rate coefficients in the temperature range from 103 to 107 K, and compared with calculated data from the literature. The experimentally derived plasma rate coefficients are 60% larger and 30% lower than the previously recommended atomic data for the temperature ranges of photoionized plasmas and collisionally ionized plasmas, respectively. However, good agreement was found between experimental results and the calculations by Gu and Colgan et al. The plasma rate coefficients deduced from experiment and calculated by the current AUTOSTRUCTURE code show agreement that is better than 30% from 104 to 107 K. The present results constitute a set of benchmark data for use in astrophysical modeling.

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].

Our prime computation effort is to support current and future measurements of atomic photoionization cross-sections being performed at various synchrotron radiation facilities around the globe, and computations for astrophysical applications. In our work we solve the Schrodinger or Dirac equation using the R-matrix or R-matrix with pseudo-states approach from first principles. The time dependent close-coupling (TDCC) method is also used in our work. Finally, we present cross-sections and rates determined for diatom-diatom and radiative collision processes between atoms and ions currently of great interest to astrophysics.

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

Author(s): Thomas, CM; Baral, KK; Aryal, NB; Habibi, M; Esteves-Macaluso, DA; Kilcoyne, ALD; Aguilar, A; Schlachter, AS; Schippers, S; Muller, A; Phaneuf, RA | Abstract: © 2017 American Physical Society. Absolute cross-section measurements are reported for single photoionization of Cn+ fullerene molecular ions (n=40, 50, 70, 76, 78, and 84) in the photon-energy range 18-70 eV. The experiments were performed by merging a mass and charge selected beam of Cn+ molecular ions with a beam of monochromatized synchrotron radiation and measuring the yield of Cn2+ product ions as a function of the photon energy. Oscillator strengths determined by integrating the measured cross sections over this energy range exhibit a linear dependence on n. The cross sections are parametrized by fits to three Lorentzian functions to represent plasmon excitations and a linear function for direct ionization. The highest-energy resonance in the data near 46 eV is similar to that previously observed in single photoionization of C60 and may be attributable to a harmonic of the dominant surface-plasmon resonance near 23 eV.

We have used a single-particle detector system, based on secondary electron emission, for counting low-energetic (~keV/u) massive products originating from atomic and molecular ion reactions in the electrostatic Cryogenic Storage Ring (CSR). The detector is movable within the cryogenic vacuum chamber of CSR, and was used to measure production rates of a variety of charged and neutral daughter particles. In operation at a temperature of ~6 K, the detector is characterised by a high dynamic range, combining a low dark event rate with good high-rate particle counting capability. On-line measurement of the pulse height distributions proved to be an important monitor of the detector response at low temperature. Statistical pulse-height analysis allows to infer the particle detection efficiency of the detector, which has been found to be close to unity also in cryogenic operation at 6 K., Accepted to Nuclear Inst. and Methods in Physics Research, A

We review experimental and theoretical efforts aimed at a detailed understanding of the recombination of electrons with highly-charged tungsten ions characterised by an open 4f sub-shell. Highly-charged tungsten occurs as a plasma contaminant in ITER-like tokamak experiments, where it acts as an unwanted cooling agent. Modelling of the charge state populations in a plasma requires reliable thermal rate coefficients for charge-changing electron collisions. The electron recombination of medium-charged tungsten species with open 4f sub-shells is especially challenging to compute reliably. Storage-ring experiments have been conducted that yielded recombination rate coefficients at high energy resolution and well-understood systematics. Significant deviations compared to simplified, but prevalent, computational models have been found. A new class of ab-initio numerical calculations has been developed that provides reliable predictions of the total plasma recombination rate coefficients for these ions., Comment: This is an author-created, un-copyedited version of an article published in Journal of Physics B: Atomic, Molecular and Optical Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6455/aa547d

30th International Conference on Photonic, Electronic and Atomic Collisions, ICPEAC XXX, Cairns, Australien, 26 Jul 2017 - 1 Aug 2017; Journal of physics / Conference Series 875, 052005 (2017). doi:10.1088/1742-6596/875/6/052005, Absolute rate coefficients for electron-ion recombination of astrophysically relevant Si9+ and Si10+ ions were measured at a heavy-ion storage ring. Hyperfine quenching of long-lived metastable levels was used for preparing practically pure ground-state beams in the storage ring. From the measured results rate coefficients for recombination of Si9+ and Si10+ ions in a plasma are derived and represented by simple parameterizations., Published by IOP Publ., Bristol

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