Light scattering study on the glass former o-terphenyl.

Combining double monochromator, tandem Fabry-Pérot interferometry (TFPI), and photon correlation spectroscopy (PCS), the full range of the dynamic susceptibility of the glass former o-terphenyl is covered (240-440 K). A time resolution of 6 ns is reached by the PCS setup, and the measuring gap between PCS and TFPI has significantly shrunk. Combined time domain data are presented, which cover 0.01 ps-100 s. Regarding the primary α-process, no recognizable change in shape and amplitude is observed, i.e., frequency-temperature superposition holds over the entire temperature range investigated. The only change in the susceptibility is the emergence of the excess wing contribution, leading to a flattening of the susceptibility minimum close to T(g). Separating relaxation contribution from fast and slow dynamics, we determine the relaxation strength 1-f(rel)(T) of the fast dynamics, which shows a cusplike temperature dependence with a crossover temperature T(c)=316±10 K. Due to relative small changes of 1-f(rel)(T) the effect is difficult to identify in f(rel)(T) itself. The crossover temperature is larger than previously reported as no extrapolation scheme is applied.