Electronically induced surface chemistry: localised bond breaking versus delocalisation

Surface photochemistry can be considerably different from the corresponding molecular photochemistry. This is due to the fact that bonding of reactants to a surface induces modifications also in reaction paths via electronically excited states. These changes are of importance in respect of both fundamental and applied research. The past 40 years have seen the development of quite detailed understanding of the underlying effects, in particular in the case of bond breaking, which shows up by desorption of neutral and charged molecules and/or fragments. Recent developments in laser technology and nanostructuring have brought renewed interest to this field. Here a survey is given of the important facts and ideas in this realm. It will be argued that the counterplay between localisation of excitations and their delocalisation by coupling is the decisive effect to be understood.