It's a heavy burden to report on heavy water

Science News, August 16, 2008 by Tom Siegried

If you pay attention in school, you can learn a lot about science.

Surely you remember, for example, that hydrogen is the simplest atom--a single proton surrounded by a single electron. And that hydrogen has a heavier form, with the proton joined by a neutron, called deuterium. And sooner or later the secret leaked out that water molecules, consisting of two hydrogen atoms plus an oxygen, might sometimes be built from deuterium instead of the ordinary lighter variety.

On a more advanced level--maybe we're in high school now--water displays some mysterious properties. Its density drops as it freezes, for instance, and it exhibits dozens of other anomalies compared with other liquids (SN: 1/26/08, p. 58).

You probably learned that many of water's oddities could be blamed on the curious "hydrogen bonds" weakly linking one water molecule to another. But it's unlikely that anybody ever mentioned what happens to hydrogen bonds in "heavy water," made with deuterium.

The answer: The hydrogen bonds are longer, by about 4 percent when [D.sub.2]O is in the liquid state. At the same time, the bonds between D and O within the molecules are 3 percent shorter than those between H and O. You will not have encountered such molecular intelligence in any textbook. For that you need Science News.

You can read about the dimensional differences distinguishing heavy from light water in a story by Davide Castelvecchi on Page 7 in this issue (or for a longer version, online at www.sciencenews.org, under Matter & Energy). The study reporting the new data, being published in Physical Review Letters, provides intriguing new clues to some of water's deep mysteries. It's a step toward answering some of the questions that chemists and physicists have long asked themselves (and dodged when posed by their students).

Such steps are not headline-makers, but they are nevertheless worthy of reporting. For those who paid attention in school, and for anyone eager to stay informed about the state of scientific knowledge, these are the nuggets of news that illustrate the subtlety of science's substance and the nuances of the scientific process. Results of this sort rarely break into the news lineup of general mass media. You won't see them in the typical daily newspaper or on that little message line scrolling across the bottom of the TV screen tuned to CNN.

You will, of course, find them reported here. Science News has different priorities.

--Tom Siegfried, Editor in Chief