Like a prehistoric insect trapped in amber. That is how a team studying the steps in fast-moving chemical reactions describes how it can "see" what is going on inside the test tube.
Instead of amber, Dr Denise Rooney, of the chemistry department at NUI Maynooth, uses frozen argon gas at just a few degrees above absolute zero. Her view of the trapped chemical reactions is in turn provided by infra-red spectroscopy.
Chemists are very interested in the intermediate steps that take place as a chemical reaction occurs. What appears to be instantaneous is usually anything but, and interesting and unusual but short-lived compounds form and re-form before the reaction stabilises and the final compound is achieved.
"If you want to improve chemical reactions and improve their efficiency it is fundamental to understand how the reactions proceed," Dr Rooney explained. "How they actually take place, that would be the drive behind the research."
The trick, she said, is to understand the structure and the "geometry" of an intermediate because it gives information about how the molecule might react and how it might end up. "It is the structure and geometry of the reagent that dictates the structure and geometry of the product. Geometry is critical and this technique allows us to understand the geometry."
The technique in question is called matrix isolation spectroscopy (MIS) and is dependent on two conditions, extreme cold and extreme vacuum. The vacuum is exceptional, one 10-millionth of a millibar, and the temperature is also extreme, minus 265. At this temperature non-reactive argon gas freezes solid and this element provides the technique's matrix.
"We have been looking at metal complexes, which have been known to be involved in catalysis and as reagents in chemical reactions," Dr Rooney said. These organo-metallic reagents are interesting because they are building blocks for important biological chemicals such as amino acids and for synthetic penicillin.
These medium-sized molecules are made of about 20 atoms. The target chemical is first mixed at one part per thousand with argon gas and this mix is slowly introduced into the MIS test rig. The low temperature causes it to deposit on a glass surface inside the rig like frost collects on a cold window pane.
The large molecules get wedged into an inert argon lattice that separates them from their neighbours. White light or filtered light to achieve a given wavelength is then targeted at this "frost" and the photons break off metal complexes from the larger molecules. The low temperatures and vacuum prevent any further reaction and the separated components are trapped in the argon. "Most reactions take some amount of thermal energy and this isn't available," Dr Rooney said. The samples can then be analysed at leisure using conventional infrared spectroscopy with the infrared source beamed in one window and the signal taken from another.
Many molecules have a "handedness", right or left, and a major challenge in synthetic chemistry is being able to make only one of these while preventing formation of the other. Knowing what these intermediate chemical steps look like might lead to better reagents that produce molecules with only the one handedness, she said.
Dr Rooney, a Queen's University Belfast, graduate, has been studying these chemical intermediates for the past five years at Maynooth, and has a team of three. MIS techniques are also being used by a colleague in her department, Dr John McCaffrey.