Librational Mode Linewidths of Thiourea

摘要

Raman spectra of polycrystalline thiourea were measured at various temperatures above and below the 169deg;K ferroelectric phase transition. No ``soft'' mode was found. The temperature dependence of two libration linewidths was analyzed by using a theory which is a combination of Ivanovet al.'s theory for Raman linewidths in molecular crystals and Brot's theory for the preexponential factor in activated reorientational processes. Agreement with theory is good as far as the reorientational contribution to the linewidth is concerned.