ABSTRACT
Typical of atom and molecule collisions is that the electronic motion can be separated from the nuclear motion. Alternative forms were developed, which in fact are proper representations of the scattering amplitude for atom and molecule collisions or collisions in which particles have hard cores. The simplest collision problem is elastic collision of two atoms. The only inelastic process in collisions of two atoms is excitation of electrons. The ideas were adapted to atom and molecular collisions retaining the Regge structure of the scattering amplitude. The contribution of these poles in the scattering amplitude is negligible. There are fewer Regge poles which significantly contribute to the scattering amplitude than the number of partial waves, while the integrals can be evaluated by methods which are quite accurate and relatively simple. The next development was the study of scattering phenomena in the presence of resonances.
