These experiments were performed in order to determine the factors that contribute to the yellowing of aqueous sodium iodide solutions. Previous research suggested that triiodide ion formation was responsible for the color formation. To isolate contributing factors we conducted three sets of experements. First, we examined whether visible or ultraviolet radiation was more effective in causing the color change. Second, the observation that NaI solutions could also become yellow when shielded from light led to experiments to study the role of oxygen. Finally wavelength dependence studies were performed to find the most effective wavelengths for color induction. Our results show that the most effective wavelengths were in the ultraviolet range and that oxygen also had am important role. Action spectra studies showed that the most effective wavelength was 360 nm. The mechanism for triodide formation from iodide photochemistry is shown to involve the transient formation of the sodide ion (Na-)in the solvation shell around the iodide ion.
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