First direct mass measurements on nobelium and lawrencium with the Penning trap mass spectrometer SHIPTRAP

Das Penningfallen-Massenspektrometer SHIPTRAP wurde gebaut um HochprÄazi-rnsionsmassenmessungen an schweren Radionukliden durchzufÄuhren, die in Fusions-rnreaktionen produziert und vom Geschwindigkeitsfilter SHIP vom Primärstrahl sepa-rnriert werden. Es besteht aus einer Gaszelle zur Abbremsung der hochenergetis-rnchen Reaktionsprodukte, einem RFQ-Kühler und Buncher zur Kühlung und Akku-rnmulation der Ionen und einem Doppel-Penningfallen-System um Massenmessungenrndurchzuführen. Die Masse wird durch die Messungen der Zyklotronfrequenz desrnentsprechenden Ions in einem starken homogenen Magnetfeld bestimmt. Diese Fre-rnquenz wird mit der Frequenz eines wohlbekannten Referenzions verglichen. Mitrndieser Methode können relative Fehler in der Größenordnung von 10^-8 erreicht werden. Kürzlich konnten die Massen der Nobeliumisotope 252-254No (Z=102) und desrnLawrenciumisotops 255Lr (Z=103) erstmals erfolgreich gemessen werden. Dies warenrndie ersten direkten Massenmessungen an Transuranen. Die Produktionrate dieserrnAtome lag bei etwa eins pro Sekunde und weniger. Die Ergebnisse der Massenmes-rnsungen an Nobelium bestätigen die früheren Massenwerte, die aus Q_alpha-Messungenrnabgeleitet wurden. Im Fall von 255Lr wurde der Massenexzess, der bis dahin nur ausrnsystematischen Trends abgeschätzt wurde, zum ersten Mal direkt bestimmt. DiesernErgebnisse sind ein erster Schritt für die an SHIPTRAP geplante Erforschung derrnRegion der Transurane. Das Hauptziel ist hierbei die Bestimmung der Endpunkternder alpha-Zerfallsketten, die in superschweren Elementen in der Nähe der vorhergesagtenrnStabilitätsinsel ihren Ursprung nehmen.

Investigation of the lithium ion mobility in cyclic model compounds and their ion conducting properties

Efficient energy storage and conversion is playing a key role in overcoming the present and future challenges in energy supply. Batteries provide portable, electrochemical storage of green energy sources and potentially allow for a reduction of the dependence on fossil fuels, which is of great importance with respect to the issue of global warming. In view of both, energy density and energy drain, rechargeable lithium ion batteries outperform other present accumulator systems. However, despite great efforts over the last decades, the ideal electrolyte in terms of key characteristics such as capacity, cycle life, and most important reliable safety, has not yet been identified. rnrnSteps ahead in lithium ion battery technology require a fundamental understanding of lithium ion transport, salt association, and ion solvation within the electrolyte. Indeed, well-defined model compounds allow for systematic studies of molecular ion transport. Thus, in the present work, based on the concept of ‘immobilizing’ ion solvents, three main series with a cyclotriphosphazene (CTP), hexaphenylbenzene (HBP), and tetramethylcyclotetrasiloxane (TMS) scaffold were prepared. Lithium ion solvents, among others ethylene carbonate (EC), which has proven to fulfill together with pro-pylene carbonate safety and market concerns in commercial lithium ion batteries, were attached to the different cores via alkyl spacers of variable length.rnrnAll model compounds were fully characterized, pure and thermally stable up to at least 235 °C, covering the requested broad range of glass transition temperatures from -78.1 °C up to +6.2 °C. While the CTP models tend to rearrange at elevated temperatures over time, which questions the general stability of alkoxide related (poly)phosphazenes, both, the HPB and CTP based models show no evidence of core stacking. In particular the CTP derivatives represent good solvents for various lithium salts, exhibiting no significant differences in the ionic conductivity σ_dc and thus indicating comparable salt dissociation and rather independent motion of cations and ions.rnrnIn general, temperature-dependent bulk ionic conductivities investigated via impedance spectroscopy follow a William-Landel-Ferry (WLF) type behavior. Modifications of the alkyl spacer length were shown to influence ionic conductivities only in combination to changes in glass transition temperatures. Though the glass transition temperatures of the blends are low, their conductivities are only in the range of typical polymer electrolytes. The highest σ_dc obtained at ambient temperatures was 6.0 x 10-6 S•cm-1, strongly suggesting a rather tight coordination of the lithium ions to the solvating 2-oxo-1,3-dioxolane moieties, supported by the increased σ_dc values for the oligo(ethylene oxide) based analogues.rnrnFurther insights into the mechanism of lithium ion dynamics were derived from 7Li and 13C Solid- State NMR investigations. While localized ion motion was probed by i.e. 7Li spin-lattice relaxation measurements with apparent activation energies E_a of 20 to 40 kJ/mol, long-range macroscopic transport was monitored by Pulsed-Field Gradient (PFG) NMR, providing an E_a of 61 kJ/mol. The latter is in good agreement with the values determined from bulk conductivity data, indicating the major contribution of ion transport was only detected by PFG NMR. However, the μm-diffusion is rather slow, emphasizing the strong lithium coordination to the carbonyl oxygens, which hampers sufficient ion conductivities and suggests exploring ‘softer’ solvating moieties in future electrolytes.rn