Why are atomic and molecular dimers so exciting?

Abstract The large number of experimental and theoretical studies devoted to atomic and molecular van der Waals dimers is here to attest for the strong interest and excitement raised in the scientific community over the past decade. One of their intriguing feature is the ability of the two constituting monomers to interact at incredibly large distances through newly evidenced processes, such as Interatomic Coulombic Decay, due to the transition from closed to open shells upon ionization. Beyond the interest for their intrinsic properties, dimers are also valuable for the large amount of information obtained on the monomers themselves, in particular in the case of collisions with ions. Indeed, one of the first striking findings was that dimers behave as two quasi-independent monomers regarding collision processes. This result triggered a series of experiments highlighting specific properties of atomic and molecular dimers, viewed alternatively as new species or as monomers in a minimal environment. They concern several fields, from electron emission to molecular fragmentation. This review presents the diverse and surprising facets of atomic and molecular dimers uncovered through ion collision experiments over the past fifteen years.