The Hydrated Electron and Absolute Values of Reduction Potentials

2 The Hydrated Electron and Absolute Values of Reduction Potentials 

The hydrated electron, e (aq), is a well-characterized chemical entity. If liquid water is subjected to irradiation by X- or y-ray quanta, electrons (photoelectrons) are released from water molecules, which thereby acquire a positive charge  

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The photoelectron retains most of the energy of the incident photon and itself produces further ionizations. It produces many more H20 +, /e pairs in losing its energy. The excess of energy possessed by the electrons so produced is used in such further ionizations until the electrons become thermalized, i.e. they have translational energies typical of the temperature of the bulk medium. Both types of ion become hydrated by interaction with the water solvent  

That the hydrated electron is a separate chemical entity has been demonstrated by the technique of pulse radi l sis This consists of subjecting a sample of pure water to a very short pulse of accelerated electrons. The energetic electrons have the same effect upon water as a beam of y-ray photons. Shortly after the pulse of electrons has interacted with the water, a short flash of radiation (ultraviolet and visible radiation from a discharge tube) is passed through the irradiated water sample at an angle of 90° to the direction of the pulse to detect the absorption spectra 

Measurements of the rate of reaction of the hydrated electron with water and the reverse process have given a value for the change in Gibbs energy for the equilibrium  

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