Aside,
covalent and ionic bonds, there’s a new chemical bond in the world.
It’s taken decades
to nail down, but researchers in Canada have finally identified a new chemical
bond, which they’re calling a ‘vibrational bond’.
This vibrational
bond seems to break the law of chemistry that states if you increase the
temperature, the rate of reaction will speed up. Back in 1989, a team from the
University of British Columbia investigated the reactions of various elements
to muonium (Mu) - a strange, hydrogen isotope made up of an antimuon and an
electron. They tried chlorine and fluorine with muonium, and as they increased
the heat, the reaction time sped up, but when they tried bromine (br), a
brownish-red toxic and corrosive liquid, the reaction time sped up as the
temperature decreased.
Perhaps, thought
one of the team, chemist Donald Flemming, when the bromine and muonium made
contact, they formed a transitional structure made up of a lightweight atom
flanked by two heavier atoms. And the structure was joined not by van der
Waal’s forces - as would usually be expected - but by some kind of temporary
‘vibrational’ bond that had been proposed several years earlier.
"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.”
But back then, the
team didn’t have the technology needed to actually see this reaction take
place, because it lasts for just a few milliseconds. But now they do, and the
team took their investigation to the nuclear accelerator at Rutherford Appleton
Laboratory in England.
With the help of
theoretical chemists from the Free University of Berlin and Saitama University
in Japan, Flemming’s team watched as the light muonium and heavy bromine formed
a temporary bond. “The lightest isotopomer, BrMuBr, with Mu the muonium atom,
alone exhibits vibrational bonding in accord with its possible observation in a
recent experiment on the Mu + Br2 reaction,” the team reports in the journal
Angewandte Chemie International Edition. "Accordingly, BrMuBr is
stabilised at the saddle point of the potential energy surface due to a net
decrease in vibrational zero point energy that overcompensates the increase in
potential energy.”
In other words,
the vibration in the bond decreased the total energy of the BrMuBr structure,
which means that even when the temperature was increased, there was not enough
energy to see an increase in the reaction time.
While the team
only witnessed the vibrational bond occurring in a bromine and muonium
reaction, they suspect it can also be found in interactions between lightweight
and heavy atoms, where van der Waal’s forces are assumed to be at play.
"The work
confirms that vibrational bonds - fleeting though they may be - should be added
to the list of known chemical bonds,”
