Vibrational dynamics inO18-substituted vitreous SiO2

Abstract

We report the polarized Raman spectra of vitreous ${\mathrm{Si}}^{18}$ ${\mathrm{O}}_2$ prepared by steam oxidation of Si in $\mathrm{H}_2^{}{}_{}{}^{18}$O. This yields the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ → ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ isotope shifts for all Raman- and nearly all infrared-active modes. The shifts of network vibrations agree very well with the predictions of a recently introduced nearest-neighbor central-force ideal continuous-random-network model, and thus confirm the utility of that simple model. The unexplained Raman-active "defect" lines reported at 495 and 606 ${\mathrm{cm}}^{-1\mathrm{}}$ in ordinary fused silica are shown to involve little or no silicon motion.