Rayleigh wing and Fourier transform infrared studies of intermolecular and intramolecular hydrogen bonds in liquid ethylene glycol

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Abstract
Depolarized low frequency light scattering and infrared data for ethylene glycol are presented. The measurements, performed in the temperature range 7–160 °C, help clarify the processes that characterize the dynamic response of the system. Rayleigh-wing data analysis suggests, through the width and intensity temperature evolution, the existence of a thermally activated process that can be rationalized in terms of a simple two-state model. The extracted activation (ΔH) and binding (ΔG) energies, have been attributed to the ‘transition’ from a gauche configuration, stabilized by an intramolecular H bond, to a simple gauche configuration. In addition, the study of the O-H stretching region, performed on ethylene glycol and on poly(ethylene glycol) by means of the Fourier transform infrared technique allows one to identify the intramolecular, H-bond imposed, sub-band, as well as to assign the various sub-bands originated by the existence of the H-bond potential. The observed dynamics are also discussed within the framework of current theories for associated liquids.