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The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher cross-sections. The main drawback of this technique is the wide angular distribution of the transfer products, which makes it challenging to catch and prepare them for precision measurements. To overcome this obstacle, we are building the NEXT experiment: a solenoid magnet is used to separate the different transfer products and to focus those of interest into a gas-catcher, where they are slowed down. From the gas-catcher, the ions are transferred and bunched by a stacked-ring ion guide into a multi-reflection time-of-flight mass spectrometer (MR-ToF MS). The MR-ToF MS provides isobaric separation and allows for precision mass measurements. In this article, we will give an overview of the NEXT experiment and its perspectives for future actinide research.
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+ ions. The resulting optimized ion bunch delivered by the assembly is characterized.
Cationic and anionic clusters of the group-14 elements carbon, silicon, germanium, tin, and lead are produced by high-vacuum laser ablation and studied with a multi-reflection time-of-flight mass spectrometer. In-trap photodissociation is performed for cluster species in the size range n=2–10. The clusters’ production rates as well as their dissociation pathways are used to probe the nonmetal–metal transition throughout the group. Carbon clusters show neutral-trimer break-off, while those of the other elements evaporate neutral monomers and, in some cases, form specific charged fragment sizes.
This thesis describes recent developments in multi-reflection time-of-flight mass spectrometry (MR-ToF MS) with ions exhibiting large masses and mass differences at an MR-ToF setup at the University of Greifswald. A series of in-trap manipulation techniques to selectively retain or eject ion bunches of multiple species with disparate mass-to-charge ratios is investigated. These highlight the possibility to correct long-term flight-time drifts using a reference ion species far away in mass from the species of interest and also the ability to use such a pair to perform single-reference precision mass determinations. In both cases, the results obtained with disparate-mass ion pairs are comparable to those known from operation with isobaric species.
In addition, an in-trap photoexcitation technique is developed and applied to study the dissociation behavior of atomic bismuth clusters (systems of some number of bismuth atoms). Compared to previous works by other groups, the probed cluster-size range is expanded for both ion polarities, resulting in a more comprehensive picture of the underlying dissociation pathways. The known significance of neutral-tetramer breakoff is confirmed, however, evidence is also found for the loss of larger neutral fragments.
Lastly, the principle of tandem high-resolution MR-ToF MS is introduced. This new method allows the study of the change in dissociation behavior of the cationic bismuth octamer resulting from substituting one of its atoms for lead. It is found that the lead-doping opens new preferential fragmentation pathways that outstrip the dominant tetramer breakoff for this specific precursor cluster size. As a first proof-of-principle experiment, the case of the cationic octamer shows that tandem MR-ToF MS is well-suited for the investigation of compound clusters.
Carbon-cluster ions are produced by laser irradiation of glassy carbon in high vacuum. In the case of positively charged species, a bimodal cluster distribution including fullerenes with cluster-size-to-charge ratios of up to a few hundred is observed. Resolving isotopologues by use of a multireflection time-of-flight mass spectrometer allows the detection and abundance determination of multiply charged clusters. It is found that mono-, di-, and tricationic fullerenes are produced, have similar size-over-charge-state ranges, and follow log-normal distributions known to be characteristic of an underlying coalescent growth. A statistical simulation is shown to reproduce the results.
Indium-cluster anions In−nare probed for delayed dissociation by photoexcitation in a multi-reflection time-of-flight device. In addition to prompt dissociation with below-microsecond decay constants, we observe reactionson timescales of several tens to hundreds of microseconds. These time-resolved decay-rate measurements reveala power-law behavior in time which can be traced back to the clusters’ energy distribution due to their productionby laser ablation in high vacuum. Modeling energy distributions from such a production allows us to connect thecluster-specific dissociation energy with the ensemble temperature through experimentally determined power-law exponents.
The combination of a linear quadrupole ion-filter and linear Paul trap operated with a rectangular guiding field for the filtering and accumulation of ions within the Mass Spectrometry for Single Particle Imaging of Dipole Oriented protein Complexes (MS SPIDOC) prototype [T. Kierspel et al., Anal. Bioanal. Chem., published online] is characterized. Using cationic caesium-iodide clusters, the ion-separation performance, ion accumulation, cooling, and ejection via in-trap pin electrodes is evaluated. Furthermore, proof-of-principle measurements are performed with 64 kDa multiply-charged non-covalent protein complexes of human hemoglobin and 804 kDa non-covalent complex of GroEL, to demonstrate that the module meets the criteria to handle high-mass ions which are the main objective of the MS SPIDOC project. The setup's performance is found to be in line with previous results from ion-trajectory simulations [F. Simke et al., Int. J. Mass Spectrom.473 (2022) 116779].