  The excitation spectrum of the density collective oscillations is computed
for multi-component molecular mixtures both with Coulomb and (repulsive)
short-range interactions. Distinct sound-like excitations appear, governed by
the short-range interaction, which differ from the ordinary hydrodynamic sound.
The dielectric function and the structure factor are also calculated. The
"two-sounds phenomenon" can be understood by means of the predictions of this
model.
