RadChem 2018

On the formation and stability of metal carbonyl complexes from superheavy elements and their homologues

15 May 2018, 17:15

1h 30m

Gallery (Casino Conference Centre)

Poster Chemistry of Actinide and Trans-actinide Elements Poster TAN

Speaker

Mr Yves Wittwer (Paul Scherrer Institute and Bern University)

Description

The chemical investigation of molecular transactinide species is still a challenging task mainly due to the low production cross sections and short half-lives of all superheavy (SHE) isotopes available so far. Despite those challenges, there is currently a lot of effort going on in this field as it promises a wealth of insights into relativistic effects, into the structure of the periodic table and into the properties of SHE atoms and molecules in general. A new approach to investigate the chemistry of transactinides is by synthesizing their corresponding metal-carbonyl compounds, which provides a number of advantages over alternative strategies. In theory, this strategy would allow the further investigation of Sg, Bh, and Hs, the very first chemical investigation of Mt as well as direct measurements of thermodynamic properties of their carbonyl compounds. A first experiment in 2014 lead to the successful synthesis of Sg(CO)${}_6$.${}^1$ Further experiments targeted at investigating the thermodynamic stability of this new compound were strongly hindered by unexpectedly low chemical yields for Sg(CO)${}_6$ and its homologues Mo(CO)${}_6$ and W(CO)${}_6$, as well as the formation of yet unidentified side products.

In order to overcome these limitations, this study aims at gaining additional understanding on the formation and survival of metal-carbonyl complexes under single-atom-chemistry-conditions. Next to determining optimized reaction conditions for future experiments with transactinides, this project also aims at gaining a general understanding of the mechanisms leading to the formation and stability of metal carbonyls. For this purpose, a ${}^{252}$Cf-source is used to produce short lived Mo-, Tc-, Ru- and Rh-isotopes as representative chemical homologues for Sg, Bh, Hs and Mt respectively. By connecting this source to a gas-loop that is filled with a gas mixture containing carbon monoxide, volatile carbonyl-complexes can be selectively and reproducibly synthesized. Those complexes are transported to a charcoal-trap by a gas-stream, where they are adsorbed until their decay can be registered by γ-spectrometry, which allows their quantification. Since this strategy is completely independent from accelerator beam-time, it is possible to execute a wide variety of experiments in a short time in order to probe the properties and responses of the carbonyl-formation-reaction to multiple physical and chemical parameters.

Here, we present results from studies of the influence of trace amounts of common impurities, of kinetic energy of the recoiling fission products, of pressure variations and of overall gas composition. Further studies concerning the formation and identification of side products, kinetic effects, alternative strategies for overall gas purification as well as theoretical simulations to support the experimental data are one the way.

[1] J. Even et al, Science 345, 1491 (2014)