What's a "molecular movie"?

04 July, 2015

It is a dream of the molecular sciences to record movies of molecules in action, i.e., undergoing chemical reactions, with atomic resolution. These molecular movies would provide a clear, albeit fairly classical, slow-motion movie of the atomic displacements during the chemical rearrangement.

Sketch of the chemical dynamics that could be unravelled through the experimental recording of a molecular movie, e.g., the isomerization of stilbene. (Image credits: Nele L. M. Müller, CFEL/DESY)

Obviously, it is necessary to obtain images with spatial resolution smaller than the typical spacing of atoms in molecules, i.e., on the order of 100 pm or better. Simultaneously, a high temporal resolution is neceesary to observe all atomic motions during the various elementary steps of the chemical reaction; typically, temporal resolutions on the order of 10 fs to 10 ps are necessary, but for (bio)chemical reaction with very large atomic displacements even slower temporal resolution might be satisfactory.

While static structures with femtometer resolution and time-eveolutions with femto- or even attosecond resolution have been experimental demonstrated – independently, one or the other – we are still working on the generation of the first real molecular movies that provide both simulataneously. Ultrashort pulses of short-wavelength radiation, e.g., x-rays or electrons, can provide the necessary ingredients for the recording of atomically resolved structures with few-femtosecond temporal resolution. We are at the verge of experimentally recording such movies right now, and highly controlled samples as well as modern x-ray and electron diffraction facilities are the major ingredients.

See our recent review regarding a discussion of what "molecular structure" is to begin with and this news article regarding a current article in which the recording of a molecular movie was claimed – and actually obtained computationally. Nevertheless, this experiment, together with many others before, shows the meandering route toward success.