The first step in the conversion of light into chemical or mechanical energy is the absorption of light by a molecule, resulting in a change of the molecule’s structure. The structure of the initial and final states of the molecule are usually known, but the transition between the two often happens so quickly that scientists have to rely on theoretical simulations to determine the dynamical structures. That is, one can see where an isolated molecule started and where it ended up, but one is left wondering how it got from one configuration to the other. This missing information is central to understanding how molecular reactions take place and to developing the tools to control them. Michael Minitti and colleagues [1] from SLAC National Laboratory, California, have now taken an important step towards imaging transient states by using femtosecond (fs) high-energy x-ray pulses to probe a reaction that takes place on a time scale on the order of fs.


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