Charge transfer between Rydberg atoms and polar molecules or clusters

Electron transfer collisions between state‐selected Rydberg atoms and polar closed‐shell molecules or molecular clusters is a very efficient way to create ground‐state dipole‐bound molecular anions. This process can be selective with respect to the total electric dipole moment of the neutral parent and is well understood in terms of a ionic‐covalent curve‐crossing model. It is also a very gentle and reversible way to ionize polar molecules or clusters, with minimal change of the neutral geometry. The application of Rydberg charge exchange to the isomeric selection of small size‐selected polar molecular clusters is discussed.