Based on the continuous medium theory, the Stokes shift response function of coumarin in water was investigated using the solvation energy and the spherical cavity approximation. The experimental data of the dielectric spectrum of water has been fitted to a theoretical formula with which the correlation function is calculated. Introducing a retardation time of emission of fluorescence after the vertical excitation of system led to a desirable agreement between the theoretical calculation and the experiment for the correlation function. Considering the importance of the low-frequency response in the solvation relaxation, the influence of the low-frequency polarization on the correlation function has been discussed.

Key words: Stokes shift, dielectric spectrum, solvation correlation function