COMPLETE EXPERIMENTS IN ELECTRON-ATOM IMPACT EXCITATION - PRESENT STATUS AND FUTURE-PROSPECTS

An overview is given of the present understanding of excitation in ele ctron-atom collisions, with particular emphasis on the extent to which a ''perfect scattering experiment'' in the Bederson sense has been ac hieved. Recent experimental and theoretical results are put into a com mon framework, generalizing the ideas and systematics, presented in a review paper, of the case of excitation by spin-polarized electron bea ms. For various levels of complexity, complete sets of coherence param eters are suggested, and their relationships to generalized Stokes par ameters and generalized STU parameters are pointed out.