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Simulated hydrogen flows free of friction.

Helium is one of a select group of substances that at low temperatures can form superfluids, liquids that flow without friction. A new computer simulation demonstrates that molecular hydrogen could gain entry into that exclusive club.

Researchers modeled the movement of hydrogen molecules on a flat silver surface dotted with alkali metal atoms such as potassium or cesium. The simulation shows that in this environment the hydrogen chills into a superfluid at 1.2 kelvins, just above absolute zero.

By themselves, hydrogen molecules solidify readily at low temperatures because they attract each other strongly. In the computer simulation, the alkali atoms, spaced about 1 nanometer apart, separated the hydrogen molecules and thus kept the substance liquid. "On the silver surface," says David M. Ceperley, "the alkali atoms naturally sit where we need them to be."

He and M. Carmen Gordillo, both at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, report their findings in the Oct. 20 Physical Review Letters.

The simulation traced out the paths of a group of hydrogen molecules and showed that many of them swapped positions as they moved among the alkali atoms. Molecules that change places freely constitute a portion of a liquid that can flow with no resistance--a superfluid, says Ceperley.

Simulations could explore other unusual superfluid systems, such as mixtures of CO) two fluid components, Ceperley says. This particular simulation suggests how researchers might try to produce superfluid hydrogen in the laboratory.
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Author:Wu, C.
Publication:Science News
Article Type:Brief Article
Date:Oct 18, 1997
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