Definitions and properties of generalized collision cross sections

A unified classification of binary collision cross sections is presented. This is accomplished with the aid of a collision superoperator, in terms of which both differential and kinetic theory cross sections are defined. Connections and comparisons are then made with standard expressions for chemical reaction cross sections and with those ’’spectral’’ cross sections describing collisional widths, shifts and overlapping of spectral lines. A detailed treatment of rotational invariance is included. Finally, it is shown how this general framework encompasses the more complicated cross sections that arise in the study of the field dependence of gas transport coefficients.