13-07U

Matrix elements of the linearized collision operator of linearized kinetic theory for dense gaseous mixtures with multistep interaction are found in the approximation of several first Sonine-Laguerre polynomials. They are expressed in terms of omega-integrals referred to the whole multistep potential. Pair-collision cross-sections for descending, ascending, and reflection processes on a step are obtained as functions of the relative velocity of particles. New types of cross-sections for the descending and ascending processes are revealed which concern with change of absolute value of the relative velocity only. Corresponding partial omega-integrals are found as dependences on a step height and temperature.