Electron-ion collision processes

Almost by definition, electron-ion collisions are critically important in neutral plasmas, and one must have a quantitative knowledge of these collisions to model and understand non-LTE plasmas. Experimental studies of such processes have been carried out for more than 30 years now, giving necessary input and feedback to theoretical studies so that ultimately plasmas ranging through those in astrophysical bodies, to those in controlled fusion devices, planetary atmospheres, flames, lasers, plasma generators and lighting devices can be modelled and understood. The challenge is a huge one for both the experimental and theoretical workers, since the number of processes is large: including elastic scattering, excitation, ionization and recombination for atomic ions. One has found that for each of these there are generally a number of mechanisms operative to lead to the final state. The processes are often referred to as open-quote open-quote direct close-quote close-quote and open-quote open-quote indirect close-quote close-quote processes. For molecular ions the multiplicities of mechanisms and parameters increases almost discouragingly; since the effects of internuclear motions can enter prominently into both the target and product states. It goes without saying that the number of species is essentially limitless. Thus, despite the long time of study and much progress, there remains much to be done to achieve the quest. The author in this brief space tries to give some indication of the status of a number of processes by describing some of the forefront experimental work presently going on and indicating some problems remaining to be overcome. There is no attempt to review all data and work in the literature. copyright 1996 American Institute of Physics