Classical Theory of Atomic Scattering

TLDR: In this paper, the authors describe the classical theory of atomic scattering and compare it with close coupling and variational methods for the case when the number of quantum states involved in a collision is small.

Abstract: Publisher Summary This chapter describes the classical theory of atomic scattering. When classical methods are applied to such collisions, they complement close coupling and variational methods, which are more appropriate when the number of quantum states involved in a collision is relatively small. A classical theory of atomic scattering requires the choice and interpretation of a classical model, and the solution of the classical model collision problem. No distinction is made between different states of excitation in defining the channel, as the classical energy has a continuous range of values. In practice, the initial states of atomic systems cannot be controlled sufficiently to study individual collisions precisely. Observed physical phenomena depend on statistical properties of ensembles of collisions, that is to say, on very large numbers of collisions, with variable initial states whose probability distribution is determined by the macroscopic conditions. For direct excitation of low-lying states, the method is usually less satisfactory because the energy transfer is small, and there is a large amount of ambiguity in choosing the final state energy band. It is also difficult to see how to split up this classical energy band, so as to represent the various possible quantized angular momentum final states separately.