A procedure is outlined to determine high-frequency spectra of classical liquids interacting via Lennard-Jones and similar potentials and applied to the problem of vibrational energy relaxation. The theory is based on analytical expressions derived for spherical particles in gases [Paper I, D. Schwarzer and M. Teubner, J. Chem. Phys. 116, 5680 (2002)] and is extended to the dense liquid phase by considering binary collisions in the potential of mean force. The calculated spectra are in good agreement with those derived from classical trajectory and molecular dynamics simulations. (C) 2003 American Institute of Physics.