Photochemical reaction models

Ground-state reactions are easily modeled using the absolute reaction-rate theory and the concept of the activated complex. The reacting system, which may consist of one or several molecules, is represented by a point on a potential energy surface. The passage of this point from one minimum to another minimum on the ground-state surface then describes a ground-state reaction, and the saddle points between the minima correspond to the activated complexes or transition states. 

For a theoretical discussion of photochemical reactions at least two potential energy surfaces are required the ground-state surface with reactant and product minima as well as the excited-state surface on which the pho-toreaction is launched. Furthermore, the theoretical model must be capable of describing what happens between the time of light absorption by a molecule in its electronic ground state and the appearance of the product molecule, also in its electronic ground state, and in thermal equilibrium with its surroundings. 

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