The monophotonic excitation spectrum Of C-60 fullerene is calculated in the framework of the extended Hubbard model by a symmetry adapted configuration interaction method with realistic electron correlation potential. The parameters of interelectronic potentialare optimized for C-60 fullerene with respect to the consistency of calculated dipole-active transitions with experimental absorption spectra in the spectral range of 2-6eV. A quantitative criterion and an original optimization procedure are proposed taking the relative importance of both spectral characteristics, transition energies and intensities, into account. A contradictory character is found in the case of the simultaneous consistence of both spectral characteristics. In view of the obtained results, the origin of the low-frequency peak in the C-60 absorption spectra is discussed.