Novel wavelength-resolved stimulated photon echo measurements on a dye molecule in solution are presented. Data are simulated within the multimode Brownian oscillator model using the spectral density of de Boeij [J. Phys. Chem. 100, 11806 (1996)] for the same solute-solvent system. For photon echo population times < 50 fs there are considerable differences between the measured and calculated data. Aided by further simulations, we conclude that these discrepancies result from dephasing dynamics of high frequency intramolecular vibrational modes not included in the previously derived spectral density.