Slow secondary relaxation process in supercooled liquids

We report on dielectric susceptibility measurements for the glass-forming systems toluene and 1-propanol, both of which exhibit slow secondary relaxation (Johari beta-process). We present a complete lineshape analysis for both alpha- and beta-process covering the real and imaginary parts. The observation of secondary relaxation in the rigid molecule toluene shows that this process is not of intramolecular origin. The beta-process is well resolved in the supercooled liquid and in the glass. Above T-g a strong temperature dependence of the relaxation strength Delta epsilon(beta) is observed. For the activation energy E-beta of many glass-forming systems we find the relation E-beta proportional to T-g.