Surface-state photoelectron transfer

Figure 18. Relative rate constant for the photoelectron transfer across the surface state as a function of bias potential. Photocurrent measured under identical conditions is shown in dotted lines.

This localized" approach lends itself to a more "chemical description of surface bonds. By no means it excludes the collective model of charge transfer theories. The latter suffered, till now, from ai incomplete knowledge of the surface states. There is no doubt that develepments in the theory of surface physics, as well as the use of modern techniques (e.g. photoelectron spectroscopy) will contribute to fill the gap between chemical and physical standpoints, and thus, will lead to decisive progress in the field of adsorption and catalysis. ... 

For Cu covered with a CU2O layer, electron transfer occurs at the oxide surface via surface states that accept the photoelectrons and transfer them at the same energy level to the empty states of the redox system (horizontal electron transfer). The photocurrent of passive Cu is diffusion limited for small redox concentrations of a few 0.0001 M and increases linearly with the concentration for small complex concentrations up to a constant level. It also increases with the thickness of the CU2O film due to the generation of more charge carriers for thicker light absorbing oxide layers. 

Band scheme for CU/CU2O with the hydrogen and vacuum scale, the [Co(NH3)6Cl] redox system, the subband and the path for transfer of photoelectrons via surface states and of electrons in the dark via the subband. (From Strehblow, Fl.-Fl. et al.. International Symposium on Control of Copper and Copper Alloys Oxidation, Rouen 1992, Edition de la Revue de Metallurgie, Paris, France, p. 33,1993.)... 

Solvation effects at the transition-state level of electron-transfer reactions is a field that is opening up by means of clusters reactions. Reactions within clusters (see Section 2.7) or at the surface of clusters (see Section 2.8) provide an experimental tool to observe the effect of gradual solvation on electron-transfer reactions. Femtosecond methods appear highly valuable for characterizing the electron transfer in reactions within clusters, since in neutral clusters the electrostatic effects of solvation will show up intensely at the electron-transfer level and for a short period of time, before the products are fully developed. In the gas phase the solvation of electrons is directly sensed by photoelectron spectroscopy, as exemplified in the (nonreactive) case of ultrafast solvation of electrons in water clusters [305]. 

---