Vibrational spectra of silica near 2400/degree/K: Measurement and molecular dynamics simulation

The nature and distribution of localized and extended structural units in vitreous materials, which can be modified through annealing, depends upon the thermal history of the melt and the time interval over which the melt is quenched to form the glassy state. Raman spectroscopy has been used to probe chemical bonding in amorphous silica as a function of temperature, pressure, and mechanical and chemical stress, and following exposure to ionizing radiation. Results are useful in developing structural models of glass based upon molecular dynamics simulation of the vibrational spectrum of the melt. Raman spectra of vitreous silica and of melts at temperatures approaching 2400/degree/K are reported in this work using a synchronous measurement technique which effectively minimizes the amount of blackbody radiation reaching the detector. Experimental results are compared with simulated spectra of the melt using molecular dynamics calculations based on a simple pairwise potential. A structural picture of vitreous and molten silica has been proposed based upon these comparisons. 4 refs., 1 fig