Mapping Atomic Motions with Ultrabright Electrons: Realization of the Chemists’ Gedanken Experiment

Abstract: With the development of ultrabright electron sources capable of literally lighting up atomic motions, the fundamental space-time limit to imaging chemistry has been achieved. The first studies focused on relatively simple systems.  Further advances in source brightness have opened up even complex organic systems and solution phase reaction dynamics to atomic inspection.  A number of different chemical reactions will be discussed from electrocyclization with conserved stereochemistry, electron transfer, spin transitions, to the recent observation of coherently directed bond formation using the classic I3- system, in a process analogous to a quantum Newton’s cradle.  These studies have discovered that these nominally 100+ dimensional problems, representing the number of degrees of freedom in the system, distilled down to atomic projections along a few principle reaction coordinates. This reduction in dimensionality appears to be general, arising from the very strong anharmonicity of the many body potential in the barrier crossing region. We now are beginning to see the underlying physics for the generalized reaction mechanisms that have been empirically discovered over time. The “magic of chemistry” is this enormous reduction in dimensionality in the barrier crossing region that ultimately makes chemical concepts transferrable