Reaction Step Models for Photoemission

A simple, mechanistic description of the overall photoprocess has evolved from a series of studies by Barker and coworkers. These pioneering studies have been able to relate the photoemission interfacial chemistry to 

The OH radical then can be reduced heterogeneously at the electrode to form a hydroxyl ion, 

Note above that the reaction between N2O molecules and the solvated electrons is described as homogeneous. This is because the solvated electrons are considered to be generated from dry (delocalized) electrons that are deposited in a zone of electrolyte, perhaps 10 A thick, adjacent to the electrode. 

Photoemission, in this instance, can be considered to involve two main stages firstly, the photoexcitation mechanism within the electrode material followed by the injection of a hot electron into the liquid phase, and secondly, the subsequent interactions of the emitted electrons with the solvent and dissolved solutes. A physical description of the excitation event itself is complex and may involve collective vibration of conduction electrons, called plasmons. In chemical terms, to successfully model absorption of a light quantum by the solid it is necessary to have a detailed knowledge of the matrix elements for transitions between states and of the fate of an electron that crosses the interface. Once ejected into the electrolyte, a series of reaction steps can be postulated for the electron. The overall process may comprise  

transition of hot electrons through the interface after absorption of light quanta such that both energy and momentum are conserved  

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