EFFECT OF SUCCESSIVE PERTURBATION ON PHONON BANDS IN AN ORGANIC ALLOY

Abstract

Phonon bands in mixed crystals of p-dihalobenzene series $(p-C_{6}H_{4}XY$, with $X$ and $Y = Cl, Br, I)$ have been studied by laser Raman spectroscopy. The method of successive perturbation (increase in the halogen size of the impurity) has been used to develop a criterion for the formation of localized phonon states in these organic alloys. The relative manifestations of the dynamic disorder (mass and force constant defects) and the static disorder (structural imperfections) are investigated by studying the phonon bands of a particular organic alloy at various compositions. The efficacy of isotopic substitution on the chemical impurity is examined in relation to isolating the role of the mass defect.