The impact theory of frequency exchange

The first component on the right-hand side controls dynamic development of the response in the same way as in Eq. (3.8), and the other two control spectral exchange due to collisions. Solution of Eq. (3.26) should satisfy the initial condition 

It is necessary to get insight into the kernel of the integral equation (3.26). Since frequency exchange is initiated by non-adiabatic collisions, it is reasonable to use the Keilson-Storer model. However, before employing kernel (1.16) it should be integrated over the angle 

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