Sometimes the only way to get a good look at something is to destroy it. When archaeologists excavate a site, they forever disrupt the context of how the artifacts they find were arranged in the ground. For gas-phase chemists, the molecules of interest are so small and move so fast that they can’t be directly imaged—unless they’re blown to bits.
X-ray diffraction and electron diffraction, cousins of the similar but less destructive crystallography techniques used for studying ordered solid samples, have found success in resolving the structures of isolated biomolecules and viruses. (See Physics Today, April 2011, page 13.) When it strikes a single molecule, the x-ray or electron pulse breaks bonds and destroys the specimen. Even so, a small fraction of the photons or electrons scatter elastically, just as they do in a crystal. From those particles’ diffraction pattern, researchers can extract structural information.
A complementary technique,...
