The impact approximation in the theory of bimolecular quasi-resonant processes

The kinetic equation for a density matrix, which describes the relaxation of the internal states of encountering particles dissolved in an inert medium, has been derived under the following assumptions: a) the random motion of reacting particles in a liquid is considered to be a classical Markoffian process; b) the concentration of reacting particles is small enough. The equation obtained is shown to be the generalization of that of the familiar impact theory of pressure broadening for the case of any type of encountering particle motion. Our general formulae are concretized in accordance with the physical situations of rectilinear, diffusion, and stochastic jump motion of the encountering particles.