Chemical Change

This chapter discusses the processes involving excited species which lead to chemical change, i.e. reactions in which the reactants and products differ in chemical identity rather than in state of excitation. Chemical change can come about as a result of photodissociation of the absorbing molecule into fragments, direct reaction of the excited species, or spontaneous isomerization of the excited species. Photodissociation is the most obvious type of chemical change. Several mechanisms are recognized for dissociation processes; the three major routes are optical dissociation, predissociation, and induced predissociation. The chapter then looks at photosensitized reactions; intramolecular and intermolecular abstraction reactions; and photoaddition and photocyclization reactions. It also considers multiphoton photochemistry and state-to-state photochemistry.