Theory of relaxation parameters of the spectrum shape in the impact approximation-I:General consideration

•Impact broadening theory is constructed as a limit case of the Fano relaxation theory.•The general method of the set of relaxation parameters calculation is developed.•The resonance functions for the line-mixing problem solving are adduced.

The theory of relaxation parameters of the spectrum shape in the impact approximation is constructed as a limit case of the Fano general relaxation theory of pressure broadening. The Fano binary collision relaxation matrix is presented in the integral form and after the impact approximation is introduced it is expressed through the scattering matrix in the Liouville space of the absorbing molecule and the bath particle. By means of introducing the scattering matrix eigenvectors and solving the evolution equation in the matrix form, the method suitable for the calculation of the whole set of impact relaxation parameters of the spectrum shape has been developed.