Making the Molecular Movie

One of the great dream experiments in Science is to watch atomic motions as they occur during structural changes.  In the fields of chemistry and biology, this prospect provides a direct observation of the very essence of chemistry and the central unifying concept of transition states in structural transitions.  From a physics perspective, this capability would enable observation of rarefied states of matter at an atomic level of inspection, with similar important consequences for understanding nonequilibrium dynamics and collective phenomena.  This experiment has been referred to as "making  the molecular movie".  Due to the extraordinary requirements for simultaneous spatial and temporal resolution, it was thought to be an impossible quest and has been previously discussed in the context of the purest form of a gedanken experiment. With the recent development of femtosecond electron pulses with sufficient number density to execute single shot structure determinations,  this experiment has been finally realized (Siwick et al. Science 2003).  Previously thought intractable problems in attaining sufficient brightness and spatial resolution, with respect to the inherent electron-electron repulsion or space charge broadening, has been solved. With this new level of acuity in observing structural dynamics, there have been many surprises and this will be an underlying theme.  Several movies depicting atomic motions during passage through structural transitions relevant to condensed phase dynamics will be shown (Sciaini et al. Nature, 2009, Ernstorfer et al. Science 2009, Eichberger et al Nature 2010, Jean-Ruel, J Phys. Chem. A 2011).  The primitive origin of molecular cooperativity has also been discovered in recent studies of molecular crystals.  These new developments will be discussed in the context of developing the necessary technology to directly observe the structure-function correlation in biomolecules - the fundamental molecular basis of biological systems. 

The future is even brighter with the advent of a new concept in relativistic electron guns that will open up direct observation of atomic motions in solution phase to gas phase systems with 10 femtosecond time resolution to watch even the fastest atomic motions. Some of the important scientific problems to be addressed with ultrabright electron sources will be discussed to give an impression of the potential impact of this emerging field.