Outgoing from the VLASOV-BOLTZMANN model of atomic motion in classical systems [1] the scattering law S(k, ω) is calculated. The variations of the width of the quasielastic peak are yielded without using of arbitrary additional terms to the convolution approximation. The comparison with the simple BG-model points clearly the influence of the VLASOV term on collective motions. The picture of S(k, ω) shows the existence of a second BRILLOUIN zone. With this theory experiments can be described, though no parameters are introduced in the calculations.