The photodissociation of triiodide anion (I3-) is a classic textbook reaction that has been extensively studied both in solution and in gas phase. However, probing the ultrafast dynamics of this reaction in the solid state is challenging due to partial reversibility of the reaction and its sensitivity to experimental conditions. Now, a team of scientists have discovered a new reaction intermediate, the tetraiodide radical anion (I4•-), formed as a result of the unique ordering of in the crystal lattice to direct the dissociating I atom in a process reminiscent of a quantum Newton’s cradle. They have published their results in Nature Chemistry.