A comparison of the far-infrared and low-frequency Raman spectra of glass-forming liquids

Far-infrared and low-frequency Raman spectra in the wavenumber range from 1 5 to 500 cm(-1) were recorded for glycerol, triacetin (glycerol triacetate) and o-terphenyl at temperatures from 253 to 355 K. The far-infrared spectr a of glycerol appear complex compared with the spectra of triacetin owing t o the presence of hydrogen bonding in glycerol. The experimental results ob tained for o-terphenyl are in good agreement with normal mode analyses carr ied out for crystalline o-terphenyl (A. Criado, F.J. Bermejo, A. de Andres, J.L. Martinet, Mel. Phys. 82 (1994) 787). The far-infrared results are com pared with the low frequency Raman spectra of these three glass-forming liq uids. The difference in temperature dependences found from these spectra is explained on the basis of different temperature contributions of the relax ational and vibrational processes to the low-frequency vibrational spectra. (C) 1999 Elsevier Science B.V. All rights reserved.