Two-photon photoprocesses in molecular systems

A review of two-photon photoprocesses of polyatomic molecules in the condensed phase is presented. The mechanism and the kinetics of absorption of the second photon of light are discussed, as well as the features of the main two-photon processes (ionization, electronic excitation energy transfer, dissociation with abstraction of hydrogen atoms and molecular products). The research capabilities of the method are demonstrated. It is emphasized that one of the main requirements to molecules of effective light stabilizers for polymers is the absence of two-photon processes for these molecules, which is provided by the nonradiative conversion processes initiated by reversible adiabatic reactions. On this basis, interpretation of the properties of the main classes of light stabilizers for polymers is given.