Atomic Tug of War

July 2, 2008

Still of Trajectory 3: forward scattering, clockwise rotation. Credit: Eckart Wrede

A new form of energy-transfer, reported today in Nature (3 July 2008) may have implications for the study of reactions going on in the atmosphere, and even for those occurring in the body.

Imagine a simple molecule consisting of two atoms as being like two balls attached together by a spring. If an incoming atom strikes one side of the molecule, the spring compresses and you would expect the molecule to jump backwards – remember Newton's cradle? (http://en.wikipedia.org/wiki/Newton's_cradle)

However, research by Dr Stuart Greaves in the Chemistry department at the University of Bristol, suggests that, contrary to expectations, in certain conditions the molecule jumps forwards, not backwards.

Greaves and his colleagues studied fast hydrogen atoms colliding with supersonically cooled deuterium-deuterium molecules. On the occasions when the collision did not result in a chemical reaction, the hydrogen atoms scatter.

In these 'inelastic' processes, the scattering of the hydrogen atom is normally backwards. But in this case, the team found that the inelastic scattering process led mainly to forward scattering – the opposite of what was expected.

Stuart Greaves said: "The reaction under study is the simplest chemical reaction possible and yet it still continues to surprise us, even after 80 years of scientific investigation. Our work provides another vital piece of the jigsaw for understanding the mechanics of chemical reactions, such as those going on in the atmosphere."

The explanation of what is happening is that even if the hydrogen atom flies past the deuterium-deuterium molecule in a 'grazing collision', this can tug on the deuterium atom nearest to it, thereby extending the bond connecting the two deuterium atoms, which causes the molecule to move forwards.

Link to animations: http://www.dur.ac.uk/eckart.wrede/QCT/inelastic/traj.php?product=4&traj=1

Citation: Vibrational excitation through tug-of-war inelastic collisions, by Stuart J. Greaves, Eckart Wrede, Noah T. Goldberg, Jianyang Zhang, Daniel J. Miller & Richard N. Zare. Nature, 3 July, Vol 454, p. 88.

Source: University of Bristol

• superhuman - Jul 02, 2008
  • Rank: 1.5 / 5 (6)
  "A new form of energy-transfer" it is not.
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• Mombo_Dogface - Jul 03, 2008
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  superhuman, could you explain? If your going to make comments please elaborate. My 5 year old could make those statements.
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• Latrosicarius - Jul 03, 2008
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  So, the nucleus of each atom is being attracted to the other?
  
  Whatever happend to proton-proton repusion?
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• Ragtime - Jul 03, 2008
  • Rank: 3 / 5 (2)

  superhuman, could you explain?

  Superhuman is right at the point, these simulations are using well known quantum mechanics models, here's nothing new from physical point of view. This mechanism is known for years as "anomalous nonelastic scattering".
  
  Such approach is bulvarizing science, thus dissipating the readers attention by the same way, like the "child surgery" ads mentioned above.
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