Molecular dynamics of liquid acetone determined by depolarized Rayleogh and low-frequency Raman scattering spectroscopy.

Slow to ultrafast dynamics of liquid acetone at variable temperature was investigated by depolarized Rayleigh and low-frequency Raman scattering spectroscopy, in the region 0–200 cm–1. A detailed analysis was performed on the spectra and the corresponding time responses, and a consistent view of the molecular dynamics of this important solvent was achieved. Slight effects of temperature on the spectra were interpreted, and distinct dynamical processes identified. At very low frequencies, or long time scales, acetone dynamics is characterized by a slow diffusive reorientation obeying the Stokes-Einstein-Debye hydrodynamic theory in the limit of subslip boundary conditions. An alternative model based on the microviscosity concept proved able to reproduce this correlation time and its temperature dependence. A comparative analysis of collective with single-molecule reorientational times, estimated from intramolecular Raman profiles, led to an orientational correlation parameter g2 of unity, which denotes a statistical disorder of molecular polarizability tensors. A fast local restructuring process is putatively responsible for an additional contribution identified at subpicosecond time scales, often referred to as intermediate response in other molecular liquids. The high frequency portion of the dynamical susceptibility showed the signature of librational intermolecular motions, giving rise to an ultrafast decay of the time correlation function of polarizability anisotropy. The overall approach, which provided valuable information on the dynamics, structure and molecular interactions in acetone, will be applied to complex systems such as ionic acetone solutions in a forthcoming paper.