DEPOLARIZED DYNAMIC LIGHT-SCATTERING-STUDIES OF ORTHO-TERPHENYL DYNAMICS ABOVE T(G)

Depolarized Rayleigh spectra of ortho-terphenyl (OTP) were measured in the temperature range from T(g) to T(g) + 190 K. Two samples prepared with and without "clusters" were used for the measurement. Four different Fabry-Perot interferometers covering the time range from about 0.5 ps to 100 ns were employed. Two relaxation modes were observed: a slow mode with all its characteristics of the alpha-process, and a fast mode with a constant, temperature independent relaxation time of about 3 ps. The fast mode has not been reported heretofore. The intensity of the fast mode vanishes at about the Vogel-Fulcher-Tamman temperature T0. The relaxation times of these two processes are found to be identical for both OTP with and without clusters. The temperature dependence of the relaxation time of the alpha-process is Arrhenius at high temperatures, but shows a Williams-Landel-Ferry (WLF) behavior in the range from T(g) to T(g) + 80 K for both samples with and without the long-range density fluctuations (i.e., cluster).