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Mirror-image threesomes in water molecules.

For all its global importance, water still defies thorough understanding. Scientists cannot explain many of the properties of this ubiquitous liquid, especially on a molecular scale. Thus, they cannot fully assess the role it plays in living and nonliving systems.

Until recently, scientists lacked the far-infrared lasers necessary to study the vibrational energy of the bond that exists between the hydrogen atoms of two water molecules. But with a technique called far-infrared vibration-rotation-tunneling spectroscopy, researchers have begun to pry into the secrets of these weak forces that keep water molecules together.

"Our approach is to build up liquid water one molecule at a time," says Richard J. Saykally, a physical chemist at the University of California, Berkeley. Most recently, he has examined three water molecules cooled to the equivalent of 4 kelvins. That temperature quenches any movement caused by thermal energy, making it easier to study the quantum mechanics of this triplet.

The triplet arranges with each oxygen and three hydrogen atoms forming a six-member ring along a plane. Two hydrogen atoms stick up from this ring and one hangs down. However, each triplet quickly and continuously flips back and forth between two mirror-image configurations, Saykally and Berkeley graduate student Nick Pugliano report in the Sept. 25 SCIENCE. The up-hydrogen atoms then face down and vice versa.

This motion occurs because of a quantum effect called tunneling, which allows each water molecule to rotate around the hydrogen bond that links it to a neighboring water molecule, Saykally explains. He suspects that larger clusters of water will also exist in right- and left-handed, or chiral, forms and wonders whether water's chirality may have played a role in encouraging chirality in more complex natural molecules.
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Title Annotation:infrared spectroscopy used for research
Publication:Science News
Article Type:Brief Article
Date:Oct 10, 1992
Words:283
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