Ultrafast Dynamics in Aprotic Molecular Liquids: A Femtosecond Raman-Induced Kerr Effect Spectroscopic Study

Abstract

Abstract We have studied the ultrafast dynamics of forty aprotic molecular liquids by femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. Some physical properties such as shear viscosity, density, and surface tension of the molecular liquids have also been measured. From the Fourier transform Kerr spectra in the frequency range of about 0–200 cm−1, we have found that the first moment of the low-frequency intermolecular vibrational spectrum is moderately correlated with the root of the value of surface tension divided by density. This fact indicates that the microscopic intermolecular interaction is related to the macroscopic physical property of intermolecular force in molecular liquids. On the other hand, a correlation between the first moment of the intermolecular vibrational spectrum and the interaction energy of two identical molecules is almost nonexistent. The difference between the two relations suggests that the many-body interaction effect takes a hand in the intermolecular vibrational dynamics in molecular liquids. We have also found that the shapes of the broad low-frequency vibrational spectra for aromatic molecular liquids show a clearer bimodal feature than those for non-aromatic molecular liquids. Picosecond Kerr transients for most of the molecular liquids are non-exponential. The slowest relaxation time is qualitatively explained by the Stokes–Einstein–Debye model.