In this paper we demonstrate the ability of inelastic (Raman) light scattering to probe polymerization transitions. We show that after proper treatment—that is, separating isotropic and anisotropic contributions and employing the reduced representation which removes the thermal population effect of vibrational energy levels—the Raman data can be used as an accurate quantitative indicator of monomer↔polymer transitions. In particular, we have applied this method to study the thermoreversible polymerization transition of liquid sulfur up to 300 °C. Raman spectra obtained from rapidly quenched samples over a broad low-temperature range, from −180 °C to ambient temperature, revealed the fact that the equilibrium between monomers and polymers in the solid amorphous state is precarious; thus quench-and-dissolution methods employed to determine the polymer content of the liquid are not accurate. Our data are compared with existing data obtained via quench-and-dissolution techniques showing considerable dissimilarities above 250 °C. Our experimental data seem to conform better to the equilibrium polymerization transition theories than previously reported data especially in view of the lack of a high-temperature plateau value in the extent of polymerization, although complete agreement between experiments and theory is still missing. Finally, the width of the Raman peak assigned to polymeric sulfur vibrations has been used as a rough indicator of the size distribution of sulfur chains.

In situ polarized and depolarized Raman spectra of glassy, supercooled, and molten SiO2 have been measured over the broad temperature range 77-2150 K in an effort to examine possible structural changes caused by temperature variation. A new experimental setup using a CO2 laser for heating the sample has been designed allowing measurement with controllable blackbody radiation background at temperatures up to 2200 K. Careful and systematic relative intensity measurements and the use of the isotropic and anisotropic Raman representation of the spectra revealed hidden bands in the bending mode region and resolved bands in the stretching region of the spectra. Overall the spectra behavior shows similarities with the spectra of the recently studied tetrahedral glasses/melts of ZnCl2 and ZnBr2. Increasing temperature causes subtle changes of the relative intensities within the silicon-oxygen stretching region at approximately 750-850 cm(-1) and gives rise to a new band at approximately 930 cm(-1). The spectral behavior is interpreted to indicate that the "SiO42" tetrahedra are bound to each other to form the network by apex-bridging and partly by edge-bridging oxygens. The network structure of the glass/melt is formed by mixing a variety of tetrahedra participating in "open" (cristobalitelike), "cluster" (supertetrahedra), and "chain" edge-bridged substructures bound to each other by bridging oxygens. A weak in intensity but strongly polarized composite band is resolved at approximately 1400 cm(-1) and is assigned to Si[Double Bond]O terminal bond frequency. Temperature rise increases the concentration of the terminal bonds by breaking up the network. These structural changes are reminiscent of the polyamorphic transformations occurring in silica as has recently been predicted by computer simulations. At low frequencies the Raman spectra reveal the presence of the Boson peak at approximately 60 cm(-1) which is well resolved even above melting temperature up to 2150 K.

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