STUDYING LIQUID DYNAMICS WITH OPTICAL KERR EFFECT SPECTROSCOPY

Abstract

Time-resolved optical Kerr effect (OKE) spectroscopy is an established tech-nique for studying the orientational dynamics of liquids. The reduced spectral density (RSD) obtained from transforming the OKE spectrum into the frequency domain has shown its utility in probing the intermolecular dynamics of liquids.

The intermolecular dynamics of benzene and its isotopologues have been inves-tigated using OKE spectroscopy. The observed linear dependence of the collective orientational correlation time on the square root of the moment of inertia leads to the conclusion that there is strong translation-rotation coupling in benzene liquid. By ana-lyzing of the RSDs of benzene and its isotopologues, it is evident that the librational scattering dominates the high-frequency region and plays a major role throughout the RSD.

The dynamics of confined liquids have also been studied using OKE spectros-copy. A blue shift of the high-frequency portion of the RSD of confined benzene has been observed. This blue shift is similar to the shift in the RSD of bulk benzene as the temperature is decreased. It is believed that this shift in the high-frequency portion of the RSD reflects the densification of the liquid in confinement. This phenomenon has also been observed in confined pyridine and acetonitrile liquids.

OKE spectroscopy has also been employed in studies of the dynamics of nano-confined propionitrile and trimethyl acetonitrile. The results of these studies indicate that propionitrile can form a lipid-bilayer-like structure at the confining surfaces, with the alkyl tails of the sublayers being entangled. However, due to the steric effects im-posed by the tert-butyl group in trimethyl acetonitrile, bilayers are not formed at the confining surfaces for this liquid.