By using ultra-short laser pulses to spin a cyanide molecule like a propeller, chemists at the University of Southern California and Brown University have achieved the first known demonstration of near-frictionless motion in water. Eventhough the discovery has no immediate practical use, says USC chemist Stephen Bradforth, "it impacts how we think about the vast majority of chemical reactions"--90 percent of which take place in liquid solutions.

Indeed, the technique gives chemists a potential new tool to influence how a reaction progresses, as one way to do that is to isolate an interacting molecule from its surroundings.

In experiments they describe in a recent issue of the journal Science, the chemists start with a water sample containing cyanide ions, each of which is basically a molecular stick with a carbon atom at one end and a nitrogen atom at the other. Then they spin the sticks to with a laser.

Within the first quarter-turn, each rotating cyanide ion creates a shock wave that throws back the surrounding water molecules. (Bradforth, who is part of the study team, likens the phenomenon to a passenger swinging a suitcase in a crowded airport terminal, minus the real-life bruises and hurt feelings.) Inside the resulting bubble, the molecule will then continue whirling for a time with essentially no friction.

Besides Bradforth, authors of the report included Brown University chemist Richard Stratt, graduate students Amy Moskun and Askat Jailaubekov from USC, and Guohua Tao from Brown.

Primary funding for this work came from the National Science Foundation, with additional support from the David and Lucile Packard Foundation.



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