Discrepancies between oscillator strengths (transverse effective charges) determined from LO-TO splitting and from the lineshape of E ( w ) spectra point to the influence of many-particle effects (m.p.e. ). They are discussed for phonon bands in vitreous and crystalline quartz.According to the classical theory of optical dispersion /1/ the dielectric function in the range of phonon bands can be written af; 2) Rudower Chaussee 6, DDR-1199 Berlin, GDR.