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New type of chemical bond discovered

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Move over, covalent and ionic bonds, there’s a new chemical bond in town, and it loves to shake things up. 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. The researchers, Amy Nordrum writes for Scientific American, “were flummoxed”. 
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.
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. The researchers, Amy Nordrum writes for Scientific American, “were flummoxed”. 

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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 heavy muonium and
lightweight 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,” says Nordrum at Scientific American.
Source: Scientific American

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