Bestimmung von absoluten Auger- und radiativen Zerfallsraten K-Schalen-angeregter hochgeladener Eisenionen

Die Emissions- und Absorptionslinien von K-Schalen-Übergängen in hochgeladenen Eisenionen gehören zu den bedeutendsten Charakteristika in den Röntgenspektren vieler astronomischer Objekte. Sie werden verwendet, um Eigenschaften und Dynamik heißer astrophysikalischer Plasmen zu bestimmen, wozu eine genaue Kenntnis der Übergangsraten, und insbesondere des Verhältnisses von radiativem und autoionisierendem Zerfall, benötigt wird. Diese waren bisher jedoch nur aus theoretischen Berechnungen bekannt. In der vorliegen Arbeit wurden erstmals absolute Zerfallsraten von radiativen und autoionisierenden Übergängen in lithiumartigen, berylliumartigen und kohlenstoffartigen Eisenionen experimentell bestimmt. Dazu wurden die Ionen in einer Elektronenstrahlionenfalle erzeugt und durch Röntgenstrahlung des Synchrotrons PETRA III resonant angeregt. Durch Anwendung einer neu entwickelten Messmethode, bei der gleichzeitig der Auger- und der radiative Zerfall beobachtet wurden, konnten systematische Unsicherheiten stark reduziert werden, wodurch Genauigkeiten besser als 10% erreicht wurden

Insights from 125Te and 57Fe nuclear resonance vibrational spectroscopy: a [4Fe-4Te] cluster from two points of view.

Iron-sulfur clusters are common building blocks for electron transport and active sites of metalloproteins. Their comprehensive investigation is crucial for understanding these enzymes, which play important roles in modern biomimetic catalysis and biotechnology applications. We address this issue by utilizing (Et4N)3[Fe4Te4(SPh)4], a tellurium modified version of a conventional reduced [4Fe-4S]+ cluster, and performed both 57Fe- and 125Te-NRVS to reveal its characteristic vibrational features. Our analysis exposed major differences in the resulting 57Fe spectrum profile as compared to that of the respective [4Fe-4S] cluster, and between the 57Fe and 125Te profiles. DFT calculations are applied to rationalize structural, electronic, vibrational, and redox-dependent properties of the [4Fe-4Te]+ core. We herein highlight the potential of sulfur/tellurium exchange as a method to isolate the iron-only motion in enzymatic systems

Polarization of K-shell dielectronic recombination satellite lines of Fe XIX-XXV and its application for diagnostics of anisotropies of hot plasmas

We present a systematic measurement of the X-ray emission asymmetries in the K-shell dielectronic, trielectronic, and quadruelectronic recombination of free electrons into highly charged ions. Iron ions in He-like through O-like charge states were produced in an electron beam ion trap, and the electron-ion collision energy was scanned over the recombination resonances. Two identical X-ray detectors mounted head-on and side-on with respect to the electron beam propagation recorded X-rays emitted in the decay of resonantly populated states. The degrees of linear polarization of X-rays inferred from observed emission asymmetries benchmark distorted-wave predictions of the Flexible Atomic Code (FAC) for several dielectronic recombination satellite lines. The present method also demonstrates its applicability for diagnostics of energy and direction of electron beams inside hot anisotropic plasmas. Both experimental and theoretical data can be used for modeling of hot astrophysical and fusion plasmas.Comment: 22 pages, 4 figures, 10 tables, accepted for publication in The Astrophysical Journal Supplement Serie

Weiterentwicklung eines Geschwindigkeits filters zur Beobachtung ladungsändernder Prozesse hochgeladener Ionen

Resonant photoionisation- and photorecombination processes of highly charged ions had been investigated in this work. A new design of the Wien-type velocity filter in use before, has signi cantly improved the device. This was used to separate highly charged ions extracted from an electron beam ion trap depending on their q/mratio. During a beamtime at the synchrotron radiation source BESSY II, resonant photoionisation of Fe15+ was observed and measured for the rst time. The precision of this measurements allows to test and distinguish between various predictions on a hitherto unreached level. Furthermore, several new methods based on analysis of the extracted ions which were sucessfull tested during measurements of dielectronic recombination, promise further improvements in future measurements

Highly Charged Ions for High-Resolution Soft X-ray Grating Monochromator Optimisation

The energy-resolving performance of a synchrotron radiation monochromator can be characterised by measuring the fluorescence response of a gas in scans across characteristic absorption lines. Here, we describe a method using exceptionally narrow absorption features in the soft x-ray range. The features belong to helium-like ions and examples of the transition 1s → 2p in O$^{6+}$ and Ne$^{8+}$ are shown. We describe the instrument PolarX-EBIT and show typical data. A performance with ten times sharper effective feature width, when compared to neutral-gas absorption features, is demonstrated

Sound Velocities in FeSi at Lower Mantle Conditions and the Origin of Ultralow-Velocity Zones

The origin of ultralow-velocity zones (ULVZs) remains an open question despite recent advances in mineral physics and seismology. Here, we examine the hypothesis that FeSi formed from core-mantle chemical reactions is a plausible source of ULVZs at the core-mantle boundary (CMB). The sound velocities of B2-structured FeSi were measured up to 115(2) GPa and 1600(200) K by nuclear inelastic scattering (NIS) in laser-heated diamond anvil cells (LH-DACs). Within uncertainties, the sound velocities of B2-FeSi display negligible anharmonicity, hence validating the extrapolation of velocity-density relations (Birch's law) to P-T conditions of the CMB. The sound velocities of B2-FeSi are significantly lower compared to other candidate phases in a lowermost mantle assemblage, and the Preliminary Reference Earth Model at CMB conditions. Less than 8.4 vol% of FeSi in the aggregate is thus sufficient to explain both the velocity decrements and the high density anomaly observed in a wide range of ULVZs.ISSN:0094-8276ISSN:1944-800

Insights from 125Te and 57Fe nuclear resonance vibrational spectroscopy: a [4Fe-4Te] cluster from two points of view.

Iron-sulfur clusters are common building blocks for electron transport and active sites of metalloproteins. Their comprehensive investigation is crucial for understanding these enzymes, which play important roles in modern biomimetic catalysis and biotechnology applications. We address this issue by utilizing (Et4N)3[Fe4Te4(SPh)4], a tellurium modified version of a conventional reduced [4Fe-4S]+ cluster, and performed both 57Fe- and 125Te-NRVS to reveal its characteristic vibrational features. Our analysis exposed major differences in the resulting 57Fe spectrum profile as compared to that of the respective [4Fe-4S] cluster, and between the 57Fe and 125Te profiles. DFT calculations are applied to rationalize structural, electronic, vibrational, and redox-dependent properties of the [4Fe-4Te]+ core. We herein highlight the potential of sulfur/tellurium exchange as a method to isolate the iron-only motion in enzymatic systems

Complete measurements of anisotropic x-ray emission following recombination of highly charged ions

Synopsis We report the first systematic measurement of x-ray emission anisotropies following dielectronic, trielectronic and quadroelectronic recombination into He-like through O-like iron and krypton ions. Using the experimental data we calculated the polarization of the Kα x rays in an anisotropic plasma as a function of the plasma temperature. Unexpectedly, we found that the degree of polarization is dominated by previously neglected trielectronic and quadroelectronic recombination resonances

Mössbauer, Nuclear Forward Scattering, and Raman Spectroscopic Approaches in the Investigation of Bioinduced Transformations of Mixed-Valence Antimony Oxide

Mössbauer spectroscopy, nuclear forward scattering, and Raman spectroscopy were applied to study redox transformations of the synthesized mixed-valence (III/V) antimony oxide. The transformations were induced by a culture of a hyperthermophilic archaeon of the genus Pyrobaculum. The applied methods allowed us to reveal the minor decrease of ca. 11.0 ± 1.2% of the antimony(V) content of the mixed-valence oxide with the concomitant increase of antimony(III). The method sensitivities for the quantitative assessment of the Sb(III/V) ratio have been considered