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Physical Chemistry

Frictionless pirouettes in solution

April 3, 2006 | A version of this story appeared in Volume 84, Issue 14

Given the proper push, a diatomic molecule in solution can spin with so little friction that it acts as if it were in the gas phase. That finding is the first example of nearly frictionless rotation in a room-temperature liquid (Science 2006, 311, 1907). The University of Southern California's Stephen E. Bradforth, Brown University's Richard M. Stratt, and coworkers found that when they photodissociated a flowing film of an aqueous iodine cyanide solution with ultrashort, high-energy laser pulses, they could make the resulting cyanide radical spin so quickly that it essentially wipes out any frictional force on the molecule. The spinning diatomic radical creates a shock wave that throws back the water molecules that surround it. It continues to spin nearly frictionlessly for about 10 picoseconds until the shock dissipates and the water rushes back into its space. Bradforth and Stratt say the discovery contradicts what's expected from the physics of molecules in solution and suggests chemists may need to rethink how molecules move energy around in liquids.


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