Abstract

Determining the density of states (DOS) of low-frequency modes of liquids is of fundamental importance. For instance, recent theoretical [1] and experimental [2] studies have suggested an intimate link between the low-frequency modes of a solvent and the dynamics of the chemical processes that occur within it. While it is not possible to measure directly the low-frequency DOS of a liquid, both frequency-domain techniques (such as far-infrared absorption and low-frequency Raman spectroscopy) and time-domain techniques (such as the optical Kerr effect [OKE]) provide direct means of studying subsets of the low-frequency modes. However, the interpretation of experimental data from these techniques is in general ambiguous. Both reorientational and interaction-induced processes can contribute to spectra, and their contributions may interfere with one another in some frequency ranges [3]. Even in the absence of such interference, it is difficult to assess unambiguously the degree of inhomogeneity in these formally linear spectra through lineshape analysis. Indeed, many different models may fit a given low-frequency spectrum.

© 1996 Optical Society of America