Low-Frequency Raman Spectroscopic Monitoring of Supramolecular Structure in H-Bonded Liquids

Effective density of vibrational states in H-bonded liquids was measured by Raman scattering method. Actuality of a low-frequency part of the spectrum of the intermediate (fracton) region, which obeys a power law, indicates the correct application of the percolation model. The dependence of exponent on binary solutions concentration has been studied. Existence of correlation of the fractal structure parameter and dynamic viscosity has been noted. 1. Introduction In order to explain peculiarities of the vibrational spectra of amorphous materials (aerogels, polymers, and glass), in some cases it is more effective to use fractal geometry ideas [1], which reflect an existence of large-scale self-similarity of structural inhomogeneities. Therefore, introducing “fraction” concept, which describes intermediate vibrational excitation—between acoustic and optical phonons, we have succeeded in interpretation of low-frequency spectrum portion (10–100？cm？1) as the distribution of density of vibrational states in the space with fractional dimension [2–4]. Noting [5, 6] that some molecular liquids from the viewpoint of the microstructure have common peculiarities with the amorphous medium, for example, in the water and some aqueous or nonaqueous solutions, due to the presence of hydrogen bonds between the molecules, is forming supramolecular spatial structure type of pseudopolymeric lattice with significant irregularities at microscopic scales regions—to several hundred nanometers. The existence of evidence of large-scale self-similarity within not less than two to three orders of magnitude, as well as the formal similarity of the low-frequency vibrational spectra of amorphous solids and liquids with hydrogen bonds [7], gives reason to consider the latter as a medium with fractal structure. This paper, in terms of fractal geometry, describes the features of low-frequency Raman scattering of liquids with hydrogen bonds. A type of corresponding density of vibrational states functions has been defined. Factors, which modify liquid scale self-similarity structure, have been investigated. 2. Inelastic Light Scattering by Fractal Media Percolation theory gives understanding of geometrical and topological peculiarities of unordered media (first of all liquids whose molecules are able to form hydrogen bonds) as well as understanding of cause of the large-scale structure of the self-similarity of inhomogeneities. Its application to the structure of water [8] contributed, in particular, an explanation of its thermodynamic characteristics in the bulk phase. Propagation of the