Ultracold Chemical Reactions

 

KRb Apparatus

The Team: Yu Liu, Andrei Gheorghe, Dr. Ming-Guang Hu, Dr. David Grimes

Chemical reactions can be surprisingly efficient at cold (1 mK) and ultracold temperatures (1 µK) due to the wave nature of atoms and molecules.  At these temperatures, non-classical effects such as wavefunction delocalization and tunneling through barriers, can dominate the reaction rate. A mere change of the quantum statistics of reagents at an energy typically near 10-8 kcal/mol, can further alter the reaction rate by a factor of 10 to 100.

Studies of reaction kinetics explore elementary reaction steps.  We are embarking to study unique 4-center reaction of 2 KRb -> K2+Rb2 at ultracold temperature. In KRb, the 4-center reaction which begins at 1 µK and ends with 10K exothermic energy has to transition through a very deep potential well (4000K). Such an energy mismatch between the entrance to exit channels and the intermediate transition suggests that the intermediate complex may be long-lived. Classically, one expects most reactant trajectories with a wide range of initial velocities and angles would take a long time to find their way out of such a deep potential well. This reaction, which is slow and highly unlikely classically, may proceed efficiently and prove quantum mechanics is efficient at exploring a vast range of reaction phase space. Which scenario is true awaits experimental result.

We combine atomic, molecular, and optical (AMO) physics techniques to prespare ultracold reactants and physical chemistry techniques to detect reaction products through ionization by either REMPI or velocity-map imaging.