Structure and dynamics of glass forming liquids still represent unsolved problems in condensed matter physics.When a liquid is cooled down at a rate of a few Kelvin per minute,a delayed first order phase transition into a crystalline state usually occurs 10-20 below the melting temperature.A different behavior is observed in so-called good glass formers,preferably mixtures of different molecules.They show a continuous slowing down of molecular motion from microscopic dynamics in the picosecond regime to some 100 s around the glass transition temperature T_g where molecular dynamics falls out of equilibrium on laboratory time scales.Below T_g the structure of the liquid appears to be "frozen." Nevertheless,there are secondary (so-called slow beta) relaxations in the glassy state,their nature being controversially debated.Their occurrence mostly observed as a broad dielectric absorption peak about 25 below T_g for 1 kHz measuring frequency cannot be predicted.Some small molecule,even chemically homogeneous glasses,e.g.,m-fluoroaniline exhibit a discernible (3 peak,while others like m-toluidine where fluorine is substituted by a methyl group do not.
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