In 1989, researchers investigating the properties of exotic
atoms discovered something entirely unexpected. Under certain circumstances,
the rate of a reaction paradoxically sped
up as temperature was decreased. This peculiar behavior was found to occur
between Muonium, an exotic form of hydrogen made up of an antimuon and an
electron, and bromine. Muonium’s behavior with other elements, such as chlorine
and fluorine, were more well-behaved; the reaction rate sped up as temperature
increased, exactly as expected. Bromine, however, represented a bizarre
exception.
In order to explain this mystery, scientists proposed a
model where the lighter atom formed a new sort of structure where it was
flanked by two heavier atoms, a structure that would be held together not by
normal forces but by a new sort of ‘vibrational’ bond.
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| Credit: Flemming et. al. |
"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.”
Due to the
exceedingly short lifespan of muonium, it was impossible at the time to
investigate this idea in very much depth. But with recent technological
developments, it finally became possible to answer this question with
certainty. The researchers took the question to nuclear accelerator at
Rutherford Appleton Laboratory in England.
There, they watched
the microscopic interplay unfold, and confirmed the new type of chemical bond.
It is hypothesized that this exotic new bond may take place between a variety
of ultra-light and heavy atoms. Although this new interaction is exceedingly
brief, their discovery represents an important development in our understanding
of atomic-scale physics and the chemical world.
Sources
Nordrum, Amy. "Chemists Confirm the Existence of New Type of Bond." Scientific American Feb 2015. Web.
