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| - Ultrafast Dynamics of Polar Monosubstituted Benzene Liquids Studied by the FemtosecondOptical Kerr Effect
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| - The femtosecond and picosecond dynamics of liquid aniline, nitrobenzene, and benzonitrile have been recordedthrough measurements of the optically heterodyne detected optical Kerr effect. A major part of thesubpicosecond dynamics is assigned to librational motion. This assignment is supported by studies of para-substituted benzonitrile derivatives with differing moments of inertia. The librational frequencies of the threeliquids are only weakly dependent on temperature but shift to lower frequency on dilution in inert solvents.The picosecond relaxation dynamics are well described by a biexponential function. The slowest relaxationtime behaves, at least qualitatively, as predicted by hydrodynamic models of orientational diffusion. However,quantitative analysis suggests that some of the assumptions concerning the molecular shape or hydrodynamicboundary condition are inadequate to completely describe diffusive orientational motion in these liquids.Measurements of the slowest relaxation time as a function of dilution in nonpolar solvent showed that staticorientational pair correlation is negligible in these liquids. The faster of the two picosecond exponentialrelaxation times could not be ascribed to orientational diffusion, and is instead proposed to arise from structuralrelaxation occurring on the picosecond time scale in these liquids.
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