Physical Society Colloquium

Interview for Faculty Position

Making Movies of Molecules with Ultrafast Electron Diffraction

Bradley J. Siwick

FOM Institute for Atomic and Molecular Physics
Amsterdam

Is it possible to obtain a real-time view of chemical reactions by fully resolving the elementary atomic motions that accompany the breaking and making of chemical bonds in the transition state region between reactant and product states? Or to make direct observations of the collective atomic motions leading to structural phase transitions in material systems as they take place? The experimental challenge associated with such measurements has often been referred to as "making a molecular movie" and requires the ability to study these systems on both their natural length and time scales simultaneously. For molecules, this implies atomic-level spatial resolution (~1 Å = 10^-10 m) and higher temporal resolution than any of the fundamental atomic displacements (~100 fs = 10^-13 s). The recent development of time-resolved diffraction techniques - both x-ray and electron - with ultrafast (<10-9 s) temporal resolution has opened up such a direct window on the time-evolving atomic configuration of molecules and solids. I will present some recent highlights from this newly emerging field, including pictures of the atomic configuration of a metal during a melting transition and a look at the atomic level details of protein function. Aspects of the technical challenges associated with the use of electrons in these experiments will also be discussed.