A comprehensive light scattering study of the glass former toluene

We present depolarized light scattering data of the glass former toluene as obtained from tandem Fabry-Perot interferometry and Raman scattering covering a frequency range 0.5 GHz < v < 5000 GHz. A large temperature interval of the (supercooled) liquid (T-g=117 K < T < 295 K) as well as of the glass (7 K < T < 117 K) is measured. Testing the scaling laws of idealized mode coupling theory (MCT) we find that MCT provides a satisfying interpolation up to the fluid regime (T/T-g=2.5) and a critical temperature T(c)congruent to 153 K is extracted. Deviations from the high-temperature MCT laws below T-c can be identified by constructing a master curve for the alpha-process. The deviations are attributed to spectral contributions from the high-frequency wing of the alpha-process and/or of the slow beta-process which appear apparently only below T-c. A comparison with dielectric spectroscopy data, exhibiting a strong beta-process, confirms this. Furthermore, we carry out a phenomenological analysis which assumes additivity of the susceptibility of alpha-process and fast dynamics. This approach allows us to single out the fast dynamics spectrum and to determine the nonergodicity parameter f. Whereas 1-f(T) is essentially constant above 160 K, a sharp decrease is observed below 160 K. This decrease stops at T=T-g and only a weak temperature dependence survives below T-g. Thus, the fast dynamics changes its characteristics at T-c and T-g. We speculate on the possibility of an ideal glass state exhibiting no relaxation any longer, and finally we comment on reasons for the large scatter of T-c data reported for some glass formers so far. (C) 2000 American Institute of Physics. [S0021-9606(00)50627-8].