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Friday, January 30, 2015

Scientific American= New Kind of Bonding

See InsideScientific American Volume 312, Issue 2

Chemists Confirm the Existence of New Type of Bond

A “vibrational” chemical bond predicted in the 1980s is demonstrated experimentally



Credit: Allevinatis/Flickr
Chemistry has many laws, one of which is that the rate of a reaction speeds up as temperature rises. So, in 1989, when chemists experimenting at a nuclear accelerator in Vancouver observed that a reaction between bromine and muonium—a hydrogen isotope—slowed down when they increased the temperature, they were flummoxed.
Donald Fleming, a University of British Columbia chemist involved with the experiment, thought that perhaps as bromine and muonium co-mingled, they formed an intermediate structure held together by a “vibrational” bond—a bond that other chemists had posed as a theoretical possibility earlier that decade. In this scenario, the lightweight muonium atom would move rapidly between two heavy bromine atoms, “like a Ping Pong ball bouncing between two bowling balls,” Fleming says. The oscillating atom would briefly hold the two bromine atoms together and reduce the overall energy, and therefore speed, of the reaction. (With a Fleming working on a bond, you could say the atomic interaction is shaken, not stirred.)
At the time of the experiment, the necessary equipment was not available to examine the milliseconds-long reaction closely enough to determine whether such vibrational bonding existed. Over the past 25 years, however, chemists' ability to track subtle changes in energy levels within reactions has greatly improved, so Fleming and his colleagues ran their reaction again three years ago in the nuclear accelerator at Rutherford Appleton Laboratory in England. Based on calculations from both experiments and the work of collaborating theoretical chemists at Free University of Berlin and Saitama University in Japan, they concluded that muonium and bromine were indeed forming a new type of temporary bond. Its vibrational nature lowered the total energy of the intermediate bromine-muonium structure—thereby explaining why the reaction slowed even though the temperature was rising.
The team reported its results last December in Angewandte Chemie International Edition, a publication of the German Chemical Society. The work confirms that vibrational bonds—fleeting though they may be—should be added to the list of known chemical bonds. And although the bromine-muonium reaction was an “ideal” system to verify vibrational bonding, Fleming predicts the phenomenon also occurs in other reactions between heavy and light atoms.
This article was originally published with the title "New Vibrations."
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ZhgzheJanuary 21, 2015, 7:58 AM
It's very interesting.
But I don't fully understand the last sentence in the second paragraph, which is "With a Fleming working on a bond, you could say the atomic interaction is shaken, not stirred."
Does "the atomic interaction is shaken, not stirred" mean the new chemical bond is "vibrational" instead of van der Vaals bond? 
I googled "shaken not stirred" and almost all the results are about James Bond...
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trying2help ZhgzheJanuary 28, 2015, 2:36 PM
It is a reference to James Bond. Ian Fleming was the author of the Bond series. That sentence you are having trouble understanding is just a joke.
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mrob12January 28, 2015, 8:12 PM
"It's a joke, son!"
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yoelukJanuary 28, 2015, 10:44 PM
Fascinating! Wonder new molecules could be stabilised featuring muonium instead of H. One thing the article waters down is that muonium are not really at all an isotope of hydrogen !!! The bulk of the mass of in a hydrogen atom is given by the neutron and the proton at its core which in turn are made from quarks. A muonium is made of an antimuon and an electron, its mass given by the heavy antimuon which is an elementary particle made of just it (as far as physics knows).
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FelixJanewayJanuary 29, 2015, 7:07 AM
In case anyone was looking for the paper as I was:
DOI: 10.1002/anie.201408211
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meadowaxeJanuary 29, 2015, 10:12 PM
Does someone thought in using this kind of bond in quantic computer technology?
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taygataygaJanuary 30, 2015, 3:41 AM
yoeluk, there is no neutron in a hydrogen atom unless you're talking about deuterium or tritium. The muon is also an unstable particle (mean lifetime 2.2 microseconds) and could not be used to make stable molecules. It is used as a hydrogen analogue to probe reaction mechanisms and is possible to detect due to its decay products including a positron. Its mass is approximately 1/9 that of the hydrogen atom so the mass equivalence that is central to this bonding theory is greatly exaggerated in the experimental set up.
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