ARCHIVED - NRC-led Team First to Watch a Chemical Reaction from the Molecule's Point of View

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December 05, 2005— Ottawa, Ontario

An international research team led by the National Research Council of Canada (Ottawa) has, for the first time, "filmed" a chemical reaction in real time from the molecule's point of view. The technique is described in the December 15 Web release by one of the world's leading scientific journals, Science.

The chemical processes which underlie just about everything around us involve a complex dance of both atoms and electrons. This choreography that transforms one molecule into another, however, happens at unbelievable speeds – typically within a millionth of a millionth of a second (called a picosecond, 10-12 s). Fortunately, there are ultrashort laser pulses which are even faster than this – a few hundred times faster (measured in femtoseconds, 10-15 s. One femtosecond is to one minute as one minute is to the age of the universe.). The research team announced a new approach to studying the fastest of chemical processes, but now from the molecule's point of view.

"The difference is, to make an analogy, it's as if we can now 'film' a car crash from the driver's point of view, rather than that of the traffic helicopter".
Dr. Albert Stolow, NRC-SIMS

A chemical reaction is usually represented by an arrow connecting reactants to products. The details of what happens along the arrow are the critical issue in understanding and therefore controlling chemistry. Using one femtosecond laser pulse as a starter's pistol, a second laser pulse, delayed in time, is used to clock the chemical reaction as it occurs. In this technique, a "picture" of what the molecule is doing at a particular instant is obtained by using the second laser pulse (represented by the green arrow with the flash of light) to knock off an electron. Using a combination of techniques developed at the NRC and at Sandia National Laboratories (Livermore, CA), this emitted electron can be analyzed in great detail, providing new information about the chemical process itself.

Graphic representation of a chemical reaction from the molecule's point of view.
Graphic representation of a chemical reaction from the molecule's point of view.

These photoelectron images (shown in blue) not only show the movements of the atoms during the reaction, but also the simultaneous rearrangement of the electron cloud on the molecule's frame. The details of this are only obtained when viewing from the molecule's perspective, from the so-called 'molecular frame' viewpoint.

"Femtosecond chemistry" says Dr. Albert Stolow of the NRC Steacie Institute for Molecular Sciences, "is about the ability to observe chemical reactions in 'real time' – as the atoms and electrons rearrange during the reaction. In this approach, we are now able to do this from the molecule's point of view".

From left to right, Dr. Oliver Gessner (assistant research officer), Anthony Lee (graduate student, Chemistry Department, Queen's University) and Dr. Albert Stolow (team leader and senior research officer, NRC).
From left to right, Dr. Oliver Gessner (assistant research officer), Anthony Lee (graduate student, Chemistry Department, Queen's University) and Dr. Albert Stolow (team leader and senior research officer, NRC).

The implications of this approach are that an understanding of the fastest processes which occur during the "arrow of chemistry" will lead to new thinking about the design of active materials for "molecular electronics", and understanding biological processes such as vision and photosynthesis.


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National Research Council of Canada
613-991-1431
media@nrc-cnrc.gc.ca

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