Ultrafast electron diffraction shapes up

Scientists have long dreamed of being able to study how the structure of molecules changes during complex chemical and biochemical reactions. However, direct structural information can only be achieved by scattering with X-rays, electrons and neutrons, and so far these techniques have only achieved sub-nanosecond (10-9 s) timescales. Now Ahmed Zewail and co-workers at the California Institute of Technology have developed a method of ultrafast electron diffraction that can resolve both the structure of a molecule and its dynamics during a chemical reaction in far greater detail (H Ihee et al. 2001 Science 291 458). The group now plans to investigate the structural dynamics of complex molecules, including biological structures - although the gas phase might pose a problem. In the April issue of Physics World, John R Helliwell of the Department of Chemistry, University of Manchester, UK, anticipates exciting times ahead as ultrafast spectroscopy and diffraction techniques join forces. (U.K.)