Theory of photoinduced surface reactions of admolecules

The absorption of photons by an adsorbate/substrate complex may induce a wide range of physical and chemical processes, such as desorption, dissociation and reactions. Although several of these processes have analogs in the gas phase, the presence of the surface opens new reaction pathways that are not available in the gas phase. These unique pathways can be used to control reactivity, product selectivity and yield, or to explore new reactions. Stimulated by the surge in experimental studies of surface photochemistry, various theoretical models have been recently developed to elucidate observations and explore new opportunities. In this review, we survey recent advances in the theoretical characterization of photoinduced chemical and physical processes occurring on solid surfaces, Our discussions are focused on two prototypical processes. The adsorbate photodissociation on insulator surfaces provides an ideal probe of the nonelectronic interaction with the substrate. Photochemical processes on conductors, on the other hand, highlight the excitation and relaxation processes induced by substrate hot carriers. The issues addressed here include excitation and relaxation mechanisms, the role played by internal modes of the adsorbate and energy transfer between the admolecule and the substrate. Both classical and quantum models are used in describing these processes. (C) 1999 Elsevier Science Ltd. All rights reserved.