The Theory of Collisions between Charged Particles and Highly Excited Atoms

Abstract

This chapter discusses the concept of collisions between charged particles and highly excited atoms. A highly excited atom or positive ion has an electron whose binding energy is very small in comparison with its binding energy in the ground state. The weakly bound electron has a large principal quantum number n. Because the properties of highly excited states differ so much from those of low states, the appropriate theory also differs. Systems of particles interacting through Coulomb potentials may be treated by classical mechanics in the limit as their linear dimensions become large. If one pair of particles forms a hydrogen atom or hydrogenic ion, then classical mechanics can be applied in the limit of large principal quantum number n. According to Coulomb's law, the orbital radius of a charged particle bound to another one varies inversely with the energy, so the mean Bohr radius for an H atom varies as nz. The size of an H (110) atom is typical of a small biological organism; and if solid, it could be seen easily with an optical microscope. It is as big when compared to a typical ground-state atom as a ground-state atom is compared to its nucleus. The ionic core is distinguished only by its charge and mass, except for relatively very small effects analogous to isotope effects such as hyperfine structure of ordinary atoms. To this extent, the properties of all highly excited species, with the same charge on the core and the same quantum numbers of the highly excited electrons, are the same.