Fundamentals Fundamentals
Colorless crystals of XeF4 (45 mg), react with water (crushed ice) forming
bright yellow to yellow orange polymeric XeO2, which has a half life of
approximately two minutes, at zero degrees Celsius. The newly-observed compound help explain the depletion of
xenon from could Earth’s atmosphere.
By Tyler Irving
Posted May 2011
Chemists at McMaster University have become the first in the world to synthesize and characterize XeO2, an unusual compound that could be the solution to a decades-old mystery.
In the early 1960s it was discovered that, contrary to their reputation, the heavier noble gases can form compounds under certain conditions. Xenon oxides like Xe04 and Xe03 have been known for years, but XeO2 and XeO were predicted to have marginal stabilities. David S. Brock and his supervisor Gary J. Schrobilgen wanted to test this prediction.
“When you react XeF4 with water, the final product is Xe03 and Xe gas,” says Brock, “However, if you cool it down and you do it around zero degrees Celsius, you can actually obtain a bright canary-yellow, transient solid.” Because this solid decomposes after a few minutes, it had never been characterized before. By cooling it to minus 78 degrees Celsius, Brock was able to get it to last long enough to run Raman spectra that proved it was XeO2.
The compound may explain an enduring mystery. It has been known for decades that the abundance of xenon in
our atmosphere is quite low compared with that in the solar system generally, as measured from meteorites.
Various theories have been proposed, but none could account for the full amount of Xe that was missing. In
2005, a team led by Chrystele Sanloup of Université Pierre et Marie Curie in Paris proposed that, under
certain conditions, Xe can substitute for Si in the quartz (SiO2) that forms most
of earth’s crust. Brock believes that his spectroscopic measurements of XeO2 lend
further weight to that hypothesis. “Being able to synthesize and characterize such a species that’s on the
border of stability, and how it may have implications for the missing xenon . . . that was really
fascinating.” 
Photo Credit: Gary J. Schrobilgen
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