A macroscopic sieve for Rydberg atoms

Finally, it is possible to study assemblies in which a single metal ion is trapped inside a group of rare-gas atoms stuck together to form a cluster. The properties of such an ion are similar to those of the confined atom of SommerfeId and Welker. 

The confined atom can be regarded as a first step towards modelling solids, and the problem is of current interest now that numerical methods allow more complex atoms to be studied [35]. It is also a first step towards studying the compressibility of atoms, and their ability to partake in soft chemistry (see section 11.8) [36]. 

An atomic site in a rare-gas matrix is, of course, of microscopic size. However, atoms in a beam can be excited by laser spectroscopy to extremely high n values if such a beam is pointed at a metallic grating made up of micrometre-size slits, then a cut-off will be observed in the maximum n value of the atoms which can fly through the apertures unimpeded. Such an experiment has been reported by Fabre [37] and coworkers in Paris. While it is experimentally very challenging to realise, the principle of this 

Atomic size is important in the reversible intercalation of ions in solids (see section 11.8) which has many important applications. The problem 

---