Radiationless transitions heavy-atom effect

In this section the effect of spin-orbit coupling on radiative and radiationless intercombinational transitions (transitions occurring between states of different multiplicity) will be investigated. We will be particularly concerned with the use of internal and external heavy atoms to induce spin-orbit coupling. The effect of heavy atoms on intercombinational processes occurring in aromatic hydrocarbons, carbonyl compounds, and heterocyclic compounds will be discussed. 

The rate of intersystem crossing can be increased by the presence of paramagnetic molecules such as oxygen as well as by molecules with heavy atoms such as halogen or organometallic compounds. These are concentration-dependent effects. In the case of oxygen the rate constant of a radiationless singlet-triplet transition can be written as... 

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