PHYSICISTS in Germany have measured the longest and weakest bond known
between two atoms.
Peter Toennies of the Max Planck Institute for Fluid Dynamics in
G枚ttingen and his colleagues fired a pressurised beam of ultracold helium
atoms into a vacuum to form two-atom 鈥渄imer鈥� molecules. Passing these molecules
through a fine grating produced a diffraction pattern from which the researchers
were able to calculate the size of the dimers and the strength of their bonds
(Physical Review Letters, vol 85, p 2284).
The bond between helium atoms in a dimer is 5.2 nanometres long, and has an
energy of one 10-millionth of an electronvolt, 50 million times weaker than the
bond between two hydrogen atoms. Previous attempts to measure the bonds in
helium dimers just tore them apart, says Toennies.
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