Structural and dynamic properties of liquid sulfur around the λ-transition

To gain a deeper understanding of the structure of liquid sulfur and the nature of the lambda-transition at 159 degrees C, we have performed inelastic neutron scattering (INS) experiments to yield the vibrational density of states of polycrystalline alpha-and beta-sulfur and of liquid sulfur at temperatures above (170 degrees C) and below (140 degrees C) that of the lambda-iransition, T(lambda). The data are compared with Raman spectra taken at the same temperatures. The relative intensities of the spectral features in the solid and liquid state show a significant dependence on temperature. It is concluded that the structure of molten sulfur is not describable in terms of the occurrence of distinct stable molecules. Since the local structural and INS spectral parameters for liquid sulfur below and above the lambda-transition temperature differ only slightly, it can be inferred that the difference between these two states is due to different molecular species with similar local packing properties but different thermal stabilities. A temperature-dependent dynamical equilibrium model for the liquid state seems appropriate, which might lead to a percolation transition around T(lambda) = 159 degrees C. (C) 1998 Elsevier Science B.V. All rights reserved.