  Based on the generalized non-Markovian equations obtained earlier for a
nonequilibrium one-particle distribution function and potential part of the
averaged enthalpy density [Markiv B.B., Omelyan I.P, Tokarchuk M.V., Condens.
Matter Phys., 2010, 13, 23005] a spectrum of collective excitations is
investigated, where the potential of interaction between particles is presented
as a sum of the potential of hard spheres and a certain long-range potential.
