Electron cloud mirrors fossil life-form

About a half-billion years ago, the early Paleozoic seas were filled with now-extinct creatures called trilobites, which had flat, oval, segmented shells. Recently, a team of theoretical physicists saw the trilobite’s shape in the electron cloud they’ve plotted for a hypothetical two-atom rubidium molecule.

Plot depicts the asymmetric trilobite-shaped distribution of an electron shared by two rubidium atoms in a hypothetical molecule. Greene, et al.

The image leaped out at Hossein R. Sadeghpour of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and his colleagues when they modeled a molecule that may form in Bose-Einstein condensates, which are minuscule clouds of ultracold atoms (SN: 7/15/95, p. 36). Says Sadeghpour, “We joked that the experiment was done several hundred million years ago, and we had just stumbled upon [the result].”

The shapes’ resemblance is amusing, but the proposed molecule is of genuine scientific interest, the researchers say. First, it would be huge—500 to 50,000 times larger than an ordinary two-atom molecule—though still much smaller than a trilobite. Second, it would be electrically polar. Other molecules composed of two identical atoms—for instance, molecular oxygen—have a neutral distribution of charge.

Experimenters are now considering how to excite a rubidium condensate to actually form the molecules. In the Sept. 18 Physical Review Letters, Sadeghpour, Alan S. Dickinson of the University of Newcastle upon Tyne, England, and Chris H. Greene of JILA in Boulder, Colo., present their molecule predictions. JILA is an institute of the University of Colorado and the National Institute of Standards and Technology.

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