Vibrational bond

The lightweight muonium atom would move rapidly between two heavy bromine atoms, 

“like a Ping Pong ball bouncing between two bowling balls,” 

Donald Fleming, a University of British Columbia chemist involved with the experiment says. 

The oscillating atom would briefly hold the two bromine atoms together and reduce the overall energy.

 

image credit:http://www.rsc.org/chemistryworld/2014/10/isotope-effect-produces-new-type-chemical-bond
In the vibrational bond muonium would 'bounce' between the two bromine atoms

This vibrational bond seems to break the law of chemistry that states 

if you increase the temperature, the rate of reaction will speed up.

http://onlinelibrary.wiley.com/doi/10.1002/anie.201408211/abstract
Replacing atoms electrons with more exotic sub-atomic particles

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. 
Donald Fleming suggested that the BrMuBr radical can exist, and is not merely a theoretical construct.
*Muonium (Mu) - a strange, hydrogen isotope made up of an antimuon and an electron

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.
(credit:http://www.scientificamerican.com/article/chemists-confirm-the-existence-of-new-type-of-bond/)