Effect of Temperature on, and Reproducibility of, the Charge Transfer to Solvent Spectrum of Aqueous Iodide

Abstract

THE energy E_max of the first absorption maximum for the charge-transfer-to-solvent (c.t.t.s.) spectrum of iodide in water (E_max ≡ hv_max = hc/λ_max; λ_max in water is near 230 nm) is particularly sensitive to changes in the environment, that is, temperature¹, pressure^2,3 and added co-solvent^1,2. A recent review⁵ gives theoretical models and applications of charge-transfer-to-solvent spectra. The energy E_max for the first c.t.t.s. band of aqueous iodide is known to shift to lower values as the temperature of the solution is raised⁶. For iodide in other solvents E_max has always been reported to be linearly dependent on temperature^1,5. Recently, however, values for E_max of iodide in water have been published that show deviations from linearity outside of experimental errors^5,7, namely, thermal anomalies somewhat similar to those reported by Drost-Hansen et al. for other properties of aqueous solutions⁸. The existence of these anomalies in the E_max against T curve has, however, been denied⁹.