University of Leicester eBulletin

Solution to Elusive Problem

January 2003
No 16

Scientists at the University of Leicester are on the way to solving a problem that has long beset chemists trying to study chemical reactions.

To establish reaction mechanisms the observation of reaction intermediates is vital, but they are incredibly short-lived under normal conditions, and therefore difficult to detect.   Freezing the reaction – known as matrix isolation - has been employed for many years, but produces rigid solids in which molecules are trapped and therefore motionless.

Chemistry revolves around the making and breaking of chemical bonds. Molecules must correctly orient themselves with respect to one another so that they can react, and as reaction progresses various chemical intermediates, such as free radicals, may be formed. 

At the University of Leicester Department of Chemistry a research team led by Drs Andy Ellis and Martyn Wheeler is using an exotic new solvent - liquid helium nanodroplets (LHNDs) - as an ultra-low temperature nano-laboratory.

LHNDs have some extraordinary properties. Composed of several thousand helium atoms, they only exist at a temperature close to absolute zero (0.2 K). In addition they are superfluid, which means that molecules trapped within them can still move around.

This winning combination of exceedingly low temperature with molecule mobility opens up a multitude of exciting new applications in chemistry.

Molecules that disappear in an instant under normal chemical conditions, such as free radicals, can be studied at leisure in LHNDs.

It should even be possible to bring together several free radicals to form stable complexes, a concept previously unthinkable in experimental chemistry.

Dr Ellis commented: “This is an exciting and challenging research program at the cutting edge of modern chemistry. Dr Wheeler and I will be constructing major state-of-the art apparatus which will open up new frontiers in the study of free radical chemistry and dynamics.” 

NOTE TO EDITORS:   Further information is available from Dr Andrew Ellis, telephone 0116 252 2138, fax 0116 252 3789, email

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