Terahertz spectroscopy of hydrogen-bonded glass-forming liquids

We have measured the temperature dependent changes in the terahertz spectra of three different amorphous polyols: sorbitol, glycerol and xylitol. As samples of each material are heated from temperatures well below its glass transition temperature, T_g, to temperatures close to its melting point a clear change in absorption coefficient at T_g is observed in all three samples. In addition, the spectra of sorbitol and xylitol both reveal a marked change in absorption coefficient at temperatures of 0.6 T_g. This change indicates a change in molecular mobility that we attribute to a secondary relaxation process.