A hiding place for the Earth’s missing xenon
28 April 2014
A collaboration between researchers in Jilin, China and University College London, including Professor Chris Pickard of the Thomas Young Centre and the Department of Physics and Astronomy, has identified a possible resting place for the Earth’s elusive store of noble xenon.
The atmosphere of the Earth contains far less xenon (the second heaviest noble gas) than expected. It is one of the enduring mysteries of the planetary sciences and is often referred to as the “missing xenon paradox”.
Combining advanced structure prediction techniques, and high quality quantum mechanical calculations, the research team have shown that at the pressures found in the Earth’s core both iron and nickel (its main constituents) react readily with xenon to form a variety of thermodynamically stable compounds - most importantly the cubic Fe3Xe (see Figure). Using diamond anvil cells, the conditions at the centre of the Earth can be reproduced in the laboratory. Experiments which have tried to make iron xenon compounds have never been successful, and earlier calculations made assumptions about the likely structures and found no bonding. It had been concluded that iron and xenon do not react in the Earth’s core.
Advances in structure prediction (such as ab initio random structure searching, developed by Prof Chris Pickard, and swarm based approaches pioneered by Jilin researcher Prof Yanming Ma) allow the unbiased discovery of unsuspected materials. New, more stable, xenon iron compounds were found in the current study, and the earlier conclusion overturned. Awaiting experimental confirmation of the result, their article published in Nature Chemistry proposes that the Earth’s core is a natural hiding place for the missing xenon.
Figure: Cubic Fe3Xe. At sufficiently high pressure (around those found in the Earth’s inner and outer cores) the normally inert xenon reacts readily with iron and nickel.
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