John Charles Polanyi

Physical Chemistry

Won the 1986 Nobel Prize in chemistry for using chemi-luminescence of molecules to explain energy relationships in chemical reactions

"The most exciting thing in the twentieth century is science. Young people ask me if this country is serious about science. They aren’t thinking about the passport that they will hold, but the country that they must rely on for support and encouragement."

As a physical chemist, John Polanyi studies the physics of chemical reactions — the energy states and the movements of molecules during the moment of reaction. This field of chemistry is called reaction dynamics. His work has helped answer the question, how do you get a chemical reaction to go? Do you tickle the molecules, or do you slam them together? It turns out that in some cases tickling works, in others you just have to slam them against each other.

As Polanyi says, “The importance of this work is that we have a picture of reacting atoms in the transition state.” The transition state of a chemical reaction is the brief period, often only millionths of a second long, when the starting materials have combined together but have not yet completely transformed themselves into the products of the reaction. This knowledge of reaction dynamics has allowed chemists to fine-tune reaction conditions to improve yields in chemical processes.

 

In one recent series of experiments, Polanyi and his research team worked with the chemical methyl bromide and silicon to learn how to “print” patterns of atoms. They use million-dollar scanning tunnelling microscopes that work at very cold temperatures of minus 223°C. They can manipulate and see individual molecules. Polanyi and his research team are able to weakly attach methyl bromine atoms to an underlying silicon crystal in neat, circular patterns of 12 molecules per circle. Then, by exposing the molecules to ultraviolet light, they have discovered the bromine atoms will form strong chemical bonds with the silicon underneath while the methyl part (CH3) breaks off and floats away.

Polanyi says, “We can now photoprint molecular-scale patterns permanently onto silicon chips. Could be useful.” He is fascinated by the notion that physical spacing of chemical reactions can be controlled like this. “One can dream of a molecular-scale printing press in which the pattern is present in the ink and the press is the light.” Potential future applications in the world of nanotechnology and microchip fabrication are likely.

1. The Nobel Prize-winning experiment: A lot of energy is given off when hydrogen and chlorine react to form hydrogen chloride, but nobody knew much about this energy when Polanyi arrived at the University of Toronto in 1956 and decided to study it. Little did he realize that this simple reaction would lead to a Nobel Prize 30 years later.

2. Transition state: For a brief instant at the moment of reaction, the molecules are in a transition state as they turn into new chemicals. Polanyi’s experiments led to a picture of the arrangement of atoms in the transition state. At the time, it was known that molecules had three kinds of motion: spinning or rotational energy; buzzing or vibrational energy; and the energy of movement from one point to another, or translational energy. What was entirely unknown was the relationship between these three types of energy during a chemical reaction. Polanyi’s experiments began a new field of chemistry called reaction dynamics, the prediction of the pattern of the motion of molecules in a chemical reaction.
3. Chemiluminescence: Polanyi used an infrared spectrometer to measure the light energy emitted by the newborn products of the chemical reaction. The product molecules emit a very feeble light called chemiluminescence, which Polanyi recorded. He used this information to distinguish between vibrational and rotational energies in the molecule. His understanding of light emitted by chemical reactions later allowed him to propose vibrational and chemical lasers, the most powerful sources of infrared radiation ever developed.
4. The “Lab”: Polanyi’s graduate student assistant, Ken Cashion, set up the Nobel Prize-winning apparatus and was the first to see the result of the experiment. The two researchers had to “borrow” the spectrometer from other scientists who would have been furious if they had realized how it would be dismantled and modified for the experiment.
 


ACTIVITY


MYSTERY

 

Polanyi believes that one of the great mysteries is the molecular basis of life. He thinks that in the future we will have devices that operate in the molecular dimension, allowing observations of chemical reactions under much more widely varying conditions than is currently possible. He says, “If, perhaps, you are worried that by the time today’s scientists leave the scene and your turn comes there will be nothing left to discover, stop worrying. What we know is surely only a tiny fraction of what remains to be known. At the centre of the atom, in the nucleus of the living cell and at the outer edges of the universe lie new worlds awaiting their discoverer.”


Explore Further
 

  • Mark Ladd, Introduction to Physical Chemistry, Cambridge University Press, 1998.
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  • Polanyi's personal webpage : www.utoronto.ca/jpolanyi
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  • Atkins' and Polanyi's website accompaniment for the Physical Chemistry 8e textbook.
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