Photo induced electron emission from metals

Following the discovery of the hydrated electron in radiation chemistry, the reexamination of some fields of aqueous chemistry gave rise to a new concept of primary reduction processes. This paper surveys aspects of these investigations in which it appears that e aq, as opposed to its conjugate acid (H atom), is invariably the precursor to H2 when water is reduced. Evidence is reviewed for the production of e aq (a) photochemically, (b) by chemical reduction of water, (c) electrolytically, (d) by photo-induced electron emission from metals, (e) from stable solvated electrons, and (f) from H atoms. The basis of standard electrode potentials and various aspects of hydrated electron chemistry are discussed briefly. 

For the determination of enumerated energy characteristics, use may be made (in a particular combination) of the following quantities measured by experiment threshold of photo-induced and thermal electron emission from metal to solution and from solution to vapour phase solvated electron photoionization threshold ... 

Finally, both photo-induced electron transfer from the ligand to the metal ion, resulting in a reduction of Ln into Ln with a concomitant quenching of the metal-centered luminescence, and energy back transfer (see fig. 7) have to be avoided by an adequate ligand design positioning the LMCT and triplet states sufiiciently away from the emissive state. 

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