Spin-Orbit Coupling in Molecules

German National Research Center for Information Technology (GMD), Scientific Computing and Algorithms Institute (SCAI), Schloss Birlinghoven, D-53754 St. Augustin, Germany 

Spin enters quantum chemistry for two main reasons. First, spin degrees of freedom imply a particular symmetry behavior with respect to the exchange of two identical particles for electrons, this symmetry constraint is commonly known as the Pauli principle. Second, and more relevant in the present context, there is a magnetic moment associated with spin that can interact with all other kinds of magnetic moments. 

In addition to causing fine-structure splitting, magnetic interactions may couple states of different spin multiplicities. As a consequence, so-called spin-forbidden transitions yield some intensity. Well-known examples for this phenomenon are phosphorescence and nonradiative transitions at intersystem crossings. 

Because of the importance of spin-dependent effects in molecules, it might be interesting to learn something more about spin and its interactions 

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Christel M. Marian, Spin-Orbit Coupling in Molecules. 

W. G. Richards, H. P. Trivedi, and D. L. Cooper Spin-orbit coupling in molecules... 

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