Infrared spectroscopy has been used with oxygen-18 isotopic tracer experiments to provide insight into the mechanism of formation of sulfate by the air oxidation of sulfite, thiosulfate, or tetrathionate ions. The relative amounts of each of the different isotope isomers, or isotopomers, can be observed qualitatively by their characteristic totally symmetric vibrational mode frequencies. The source of the 18O can be either dioxygen or the solvent water. By reversing the source of the isotope, one can check the results for isotopic exchange and/or impurities.
