In For what is regarding the Rautian line shape, we can find it proposed in Rautian and Sobel'man, 1967. "A simultaneous account of radiative decay and the Doppler effect involves no difficulties, since these causes of broadening are statistically independent. As we know, the correlation function in this case equals the product of the correlation functions describing each of the causes of broadening individually". But Rautian and Sobel'man are also stressing that "broadening due to interaction and that due to the Doppler effect are statistically dependent in the general case. Broadening due to interactions involves a phase shift of the atomic oscillator when the atom collides with surrounding particles. Obviously, both the phase of the oscillations and the velocity of translational motion of the atom can be altered in the same collision."