Ion trajectories have been simulated for an assembly of a linear quadrupole ion-filter and a linear Paul trap with additional pin electrodes for MS SPIDOC, a project in preparation for the study of biomolecules by single-particle imaging with X-ray pulses. The ion-optical components are based on digital RF guiding and trapping fields. In order to carefully handle biomolecules over a wide mass-over-charge range, the module presented consists of separate components for filtering and accumulation/trapping in order to select the ions of interest and to convert the beam from a continuous ion source to ion bunches, respectively, as required for the experiments downstream. The present analysis focuses on the transmission efficiency and mass resolving power of the filter, as well as the buffer-gas-pressure-dependent ion capture and thermalization in the trap for the example of a mass-to-charge ratio equivalent to hemoglobin 15 thorn ions. The resulting optimized ion bunch delivered by the assembly is characterized. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Negatively charged tin clusters offer a broad range of decay products, as observed after electron-cluster interactions [S. König, M. Wolfram, S. Bandelow, G. Marx, L. Schweikhard, Eur. Phys. J. D 72 , 153 (2018)]. To get further insight into their decay pathways, size and charge-state selected clusters Sn n - and Sn n 2- were photo-excited at the ClusterTrap setup by 532 nm Nd:YAG laser pulses. For small mono-anionic precursor clusters containing up to n ≃ 45 atoms, Sn n-7 - and Sn n-10 - are observed as preferred ionic fragments. For bigger clusters a transition to neutral monomer evaporation was found. In the case of di-anionic precursors, preferred decay products are Sn 10 - and Sn n-10 - , indicating fission similar to the case of the group 14 neighbor element lead [S. König, A. Jankowski, G. Marx, L. Schweikhard, M. Wolfram, Phys. Rev. Lett. 120 , 163001 (2018)]. Furthermore, doubly charged fragment clusters such as Sn n-7 2- are observed, originating from break-off of neutral heptamers Sn 7 , a behavior which has not been observed previously for di-anionic clusters. Graphical abstract

The present study introduces new approaches for the capture/injection and selection of ions with large mass-to-charge (m/q) differences in an electrostatic ion beam trap (EIBT) or multi-reflection time-of-flight (MR-ToF) device. While no m/q-dependent storage criterion exists for devices of this nature, the process of injecting ions into the trap relies on a timed potential switching and is therefore mass-selective to some extent. To partially circumvent this restriction, the approach of sequential capture is presented, where additional ion species are captured while already-stored ones are unaffected by the switching pulses. Specifically, it is possible to perform a full in-trap lift capture pulse while a given, already-stored ion species is reflected in a mirror potential or passes through the lift electrode itself. Additionally, the technique of ion selection by means of transversal ejection from the trap is extended to allow ion species with large m/q differences to be retained. To this end, deflector functions with different frequencies are added with an AND logic and supplied to an in-trap deflector electrode. The combination of both techniques allows the simultaneous storage of size-selected ion species with an m/q ratio surpassing 4 : 1 at the present setup, where the single-pulse lift capture is restricted to a ratio of only 1.9. (C) 2018 Elsevier B.V. All rights reserved.

Size-selected monoanionic tin clusters Snn−, n = 7 − 75, are stored simultaneously with electrons in a Penning trap to produce poly-anionic clusters by electron attachment. In addition to doubly and triply charged clusters with the size of the precursors, fragments such as Sn−n−7, Sn−n−10 or Snn−15 are observed in the lower size range (n ≲ 50). The latter come along with the clusters Sn−10 and Sn−15, probably due to fission of doubly charged clusters as in the case of the group-14 neighbor-element lead [König et al., Phys. Rev. Lett. 120, 163001 (2018)]. Furthermore, prominent doubly charged products Sn2−n−15 seem to be produced by break-off of neutral decamers, a feature not yet observed for any other dianionic cluster. In addition, while almost no monomer evaporation is observed for singly charged clusters, this process does occur for doubly charged ones.

A development in multi-reflection time-of-flight (MR-ToF) mass spectrometry is presented with which isobars are resolved by means of an offline correction with the signal of a non-isobaric ion species. The method is demonstrated for a pair of Cr-2(+) isobars with a relative mass difference of 1.8.10(-5), with either an additional, non-isobaric Cr-2(+) or a CrO+ ion appearing in the same time-of-flight spectrum, although at a different number of revolutions during the same storage time. This is in contrast to earlier applications where ToF shift corrections are performed with ions at identical revolution numbers, typically isobars that are also acting as mass-reference ions. It is shown that ions of virtually any mass simultaneously stored in the MR-ToF analyzer can be employed. This is particularly useful in situations where both the ions of interest and the reference ions for mass calibration have only small count rates not sufficient for the ToF-shift corrections. For the present system, the resolving power increases by more than a factor of two when the offline drift correction is applied. (C) 2018 Elsevier B.V. All rights reserved.

The recently introduced method of ion separation by transversal ejection of unwanted species in electrostatic ion-beam traps and multi-reflection time-of-flight devices has been further studied in detail. As this separation is performed during the ion storage itself, there is no need for additional external devices such as ion gates or traps for either pre- or postselection of the ions of interest. The ejection of unwanted contaminant ions is performed by appropriate pulses of the potentials of deflector electrodes. These segmented ring electrodes are located off-center in the trap, i.e., between one of the two ion mirrors and the central drift tube, which also serves as a potential lift for capturing incoming ions and axially ejecting ions of interest after their selection. The various parameters affecting the selection effectivity and resolving power are illustrated with tin-cluster measurements, where isotopologue ion species provide mass differences down to a single atomic mass unit at ion masses of several hundred. Symmetric deflection voltages of only 10 V were found sufficient for the transversal ejection of ion species with as few as three deflection pulses. The duty cycle, i.e., the pulse duration with respect to the period of ion revolution, has been varied, resulting in resolving powers of up to several tens of thousands for this selection technique.

Lead clusters Pb-n(+/-) in the size range between about n = 15 and 40 have recently shown to exhibit complex dissociation spectra due to sequential and competing decays. In order to disentangle the pathways the exemplary Pb-31(+) clusters have been stored and size selected in a Penning trap and irradiated by nanosecond laser pulses. We present time-resolved measurements at time scales from several tens of microseconds to several hundreds of milliseconds. The study results in strong evidence that Pb-31(+) decays not only by neutral monomer evaporation but also by neutral heptamers breaking off. In addition, the decays are further followed to smaller products. The corresponding decay and growth times show that Pb-30(+) also dissociates by either monomer evaporation or heptamer break-off. Furthermore, the product Pb-17(+) may well be a result of heptamer break-off from Pb-24(+)-as the second step of a sequential heptamer decay.

Tetra-, penta-, and hexa-anionic gold clusters have been produced in a Penning trap. Their abundances have been investigated as a function of cluster size, and critical sizes have been determined for each charge state. Previous descriptions of the polyanion abundance by means of field emission on the one hand, and by thermionic emission On the other hand, are extended to a temperature-dependent field-emission model. The latter provides an improved explanation of experimental data, in particular for tetra- and penta-anionic gold clusters. Although the present approach is still based on a temperature concept from the bulk, it demonstrates the advantage of combining both the thermal excitation of electrons and the tunneling process in the description of stability of multiply negatively charged metal clusters with respect to electron emission.

Electron-positron plasmas have been of theoretical interest for decades, due to the unique plasma physics that arises from all charged particles having precisely identical mass. It is only recently, though, that developments in non-neutral plasma physics (both in linear and toroidal geometries) and in the flux of sources for cold positrons have brought the goal of conducting electron-positron pair plasma experiments within reach. The APEX/PAX collaboration is working on a number of projects in parallel toward that goal; this paper provides an overview of recent, current, and upcoming activities.

Ion traps are versatile tools for the investigation of gas-phase cluster ions, allowing, e.g., cluster-size selection and extended reaction times. Taking advantage of their particular storage capability of simultaneous trapping of electrons and clusters, Penning traps have been applied for the production of clusters with high negative charge states. Recently, linear radio-frequency quadrupole traps have been demonstrated to be another candidate to produce polyanionic clusters. Operation with rectangular, rather than harmonic, radio-frequency voltages provides field-free time slots for unhindered electron passage through the trap. Several aspects of electron-attachment techniques by means of Penning and radio-frequency traps are addressed and recent experimental results are presented.

For the last decade the production of polyanionic metal clusters in the gas phase and the investigation of their size- and charge-state dependent properties was the main objective of the ClusterTrap experiment. An upgrading of the ion-trapping devices extends the range of anionic charge states: a recently installed Penning trap with a 12-T superconducting magnet provides an increased mass and thus cluster-size range, crucial to reach higher anionic charge states by means of the electron-bath method. Its cylindrical Penning trap is characterized and compared with respect to the previous asymptotically hyperbolical setup. In addition, polyanionic cluster production in a linear radio-frequency quadrupole (RFQ) trap has been initiated. Preliminary results for gold-cluster polyanion production in the new Penning trap, the RFQ trap, as well as the combined use of these traps are presented.

The former Berlin electron-beam ion-trap was moved to Greifswald. One of the first aims after the reinstallation was the continuation of experiments using mixed ensembles of low- and high-Z ions for further studies of the previously reported sawtooth-like oscillations of the trap plasma. First results of these studies for xenon/argon mixtures are presented.

A new type of digital ion trap is introduced, namely a Paul trap with 3-state digital driving voltages. The stability diagram has been mapped, i.e. the relative storage efficiency with respect to the trapping parameters has been measured. The results show, that the performance of the 3-state digital ion trap can be described in terms of the conventional (2-state) digital ion trap, where the trapping parameters are defined, again, according the zeroth and first order Fourier component of the driving field.

The production of poly-anionic metal clusters by simultaneous storage of electrons andcluster anions in a Penning trap has been extended to the fifth charge state. The minimumcluster size, required to attach a fifth excess electron, has been experimentallydetermined for aluminum clusters. A refined data evaluation method is proposed, redefiningthe appearance size with respect to the delayed electron emission. It has been applied tothe penta-anions as well as to previous data of poly-anionic aluminum clusters. Inaddition, new measurements of aluminum di-anions have revealed a lower minimum appearancesize than reported earlier. Comparison of the experimental results with predictions by theconducting-sphere model for the di-, tri-, tetra- and penta-anions show deviations thatare probably due to thermal excitation of the cluster anions. The cluster-size dependenceof the poly-anion abundance spectra is qualitatively reproduced by thermionicemission.