CORRELATION-EFFECTS ON RAMAN-SCATTERING FROM LOW-ENERGY VIBRATIONAL-MODES IN FRACTAL AND DISORDERED-SYSTEMS .1. THEORY

In disordered fractal or nonfractal systems, the disorder induces rapi d fluctuations of the acoustical vibrational wave functions, so that s tatistics can be used to resolve the problem of Raman scattering from localized low-energy vibrations. We derive the expressions of light-vi bration coupling coefficient, C(omega), as a function of the frequency omega, in the case of the dipole-induced dipole mechanism of suscepti bility fluctuation and for different types of correlation, from full c orrelation to no-correlation. The results are compared to the existing numerical calculations. The expressions of C(omega) are determined fo r other mechanisms of susceptibility fluctuations, depending on an int eraction propagating in the fractal.