  This chapter presents, from a quantum-mechanical point of view, a tutorial
discussion of elementary collision processes in the bulk of a gas discharge.
Instead of merely listing kitchen-made cross section formulae and unrelated
cross section data, emphasis has been given on an unified description of
elementary processes based on general principles of quantum-mechanical
multi-channel scattering theory. By necessity, the presentation is rather
dense. Technical details left out, as well as cross section data, can be found,
respectively, in the quoted original papers and the review articles,
monographs, and web-sites mentioned in the introductory remarks to this
chapter.
