engleski

RAMAN SCATTERING STUDY OF LOW-FREQUENCY MOLECULAR VIBRATIONS IN ORTHOTERPHENYL AND PERDEUTERATED ORTHOTERPHENYL

The liquid-glass transition and the properties of supercooled liquids have attracted much attention during the past decade and a number of experimental studies have been performed using the light scattering methods. Raman spectroscopy is one of the methods often used in the study of supercooled liquids and glasses, and usually the spectral region between 10 and 200 cm-1 is studied. Orthoterphenyl ( OTP ) is one of the most studied molecular glass formers which has been studied by various experimental techniques and an elaborated empirical model for the relaxations was recently proposed ("Mainz model"). In this model, besides the well known a and b relaxation processes, a number of additional relaxation processes are assumed ( microscopic/molecular, Boson peak, etc. ). In order to further elucidate the role of different relaxation processes in the formation of OTP glass phase we measured the low-frequency Raman spectra of OTP and perdeuterated OTP crystal and melt. These experiments revealed a number of low-frequency intramolecular modes in the region below 150 cm-1. The complete knowledge of the low-frequency intramolecular vibrations of OTP is important information for testing the present theories of liquid-glass transition, ( i.e. mode coupling theory etc. ) and in development of future models.

liquid-glass transition; Raman spectroscopy; ortoterphenyl

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