Isotope Effect in IR Spectra of Highly Enriched Amorphous Silicon Dioxide ASiO2 (A = 28, 29, 30)

Abstract

Samples of amorphous silicon dioxide have been synthesized from silicon with natural isotope abundance; silicon highly enriched in silicon-28, silicon-29, or silicon-30 with a degree of enrichment from 99.29 ± 0.01 to 99.9980 ± 0.0010 at %; and silicon being a mixture of silicon-28 and silicon-30. The samples were studied by IR spectroscopy. The IR spectra of the samples demonstrate a low-frequency shift of the known stretching and bending vibration absorption bands for the silicon-29 and silicon-30 isotopes by 0.1–30.1 cm^–1 compared to silicon-28. For the silicon dioxides containing a mixture of silicon-28 and silicon-30 isotopes and with natural isotope composition, there is a deviation from the linear dependence of the vibration frequency of monoisotopic samples. The positions of the absorption band maxima in the model IR spectrum of silicon dioxide have been calculated by the DFT method. The results obtained correlate with experimental data with high accuracy. The reduced mass and force constant of vibrating groups of atoms in silicon dioxide were determined, and the influence of these factors on the isotopic shift in the IR spectrum of silicon dioxide, depending on the type of vibration, was established.