MANY-BODY THEORY OF ELECTRON-SCATTERING BY EXCITED ATOMIC TARGETS - FUNDAMENTAL FORMULAS

A many-body theory of electron-impact excitation out of excited atomic states is presented. After the fundamental equations and formulas of the general theory are given, first- and second-order approximations a re introduced. In the case of the first-order theory, detailed analyti cal formulas are also developed. The physical interpretation of the fi rst- and second-order theories are presented with the aid of Feynman-t ype diagrams. Following a discussion of initial- and final-state effec ts, the many-body theory is also related to the distorted-wave approxi mation.