Direct Evaluation of the Molar Absorption Coefficient of Hydrated Electron by the Isosbestic Point Method

The knowledge of the absorption spectrum of hydrated electron is of importance in numerous pulse radiolysis studies because it is often used for dosimetry or for second-order rate constant determination. We present a direct method for the evaluation of the molar absorption coefficient of the hydrated electron. It is based on the wavelength measurement of isosbestic points during the reaction of e^–_aq with the methylviologen MV²⁺ cations which leads to the formation of MV^+•. The molar absorption coefficient of hydrated electron is obtained using the value of the molar absorption coefficient of MV^+• at the isosbestic point at 600 nm, i.e., ε_{600nm,(MV^+•)} = 13500 ± 300 L mol^–1 cm^–1. Therefore, at the maximum of the absorption spectrum of e^–_aq at 715 nm, the value is ε_{715nm,(e^–aq)} = 19700 ± 400 L mol^–1 cm^–1. The absorption spectrum of the hydrated electron has been re-evaluated and completed from 260 to 850 nm.