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.

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.


Nordrum, Amy. "Chemists Confirm the Existence of New Type of Bond." Scientific American Feb 2015. Web.