Photochemistry

In some cases the excited species may simply transfer its excess energy to a second species. This process is called intermolecular energy transfer (path v). Photosynthesis relies on intermolecular energy transfer to redistribute the light energy gathered by chlorophyll to a reaction center where the carbohydrates that nourish the plant are produced. Physical quenching (path vi) is a special case of intermolecular energy transfer in which the chemical behavior of the species to which the energy is transferred does not change. An example of a physical quencher is the walls of a container in which a reaction is confined. If the energy transfer occurs within the same molecule, for example, and if the excess electron energy is transferred into internal motion of the molecule, such as vibration, it is called intramolecular energy transfer (path vii).