Study of Sulfur Isotopes by Vibrational Spectroscopy and Quantum Chemistry

Background/Objectives: The article is devoted to the dependence of the experimental and calculated frequencies in the IR- and Raman-spectra from the molecular mass of the sulfur isotope. Methods/Statistical Analysis: The calculations of the S₈ molecules containing the different sulfur isotopes were carried out using the GAUSSIAN’03 program package. The geometries were first optimized at the gradient-corrected DFT level using the three-parameter fit of the exchangecorrelation potential suggested by Becke in conjunction with the LYP exchange potential (B3LYP). All electron 6-31G(d), and extended cc-PVTZ basis sets were used. The absence of imaginary vibration frequencies confirmed the stationary character of the structures. Findings: IR spectra and Raman spectra of the polycrystalline isotopes α^-32S, α^-33S and α^-34S were obtained. It was found that experimental frequencies of the vibrational spectra of the isotopes of sulfur decrease in a linear manner with an increasing mass of the isotope. From the experimental correlations, the oscillation frequencies for the isotope α^-36S were determined. The results obtained demonstrate that the quantum-chemical calculations are sensitive to the isotopic shifts in the vibrational spectra of sulfur isotopes and are able to assess changes in their thermodynamic properties. Applications/Improvements: The effect of a sulfur isotope shift on the change of thermodynamic parameters.