Mechanisms for long-range forces in the ''three atoms plus electron'' system

The Born-Oppenheimer approximation is used to obtain an equation for the effective interaction of three atoms bound by a single electron. For low binding energies long-range forces arise between the atoms in an ''electron+atom pair'' that lead to bound states when the size of the three-atom cluster is several tens of angstroms. A system made up of alkali metal atoms is considered as an example. (C) 1997 American Institute of Physics.