External-field magnetic interaction parameters

32Van Van Vleck, J.H. The Theory of Electric and Magnetic Susceptibilities, Oxford, England Oxford University Press, 1932. 

84Gor Gordy, W., Cook, R.L. Microwave Molecular Spectra, New York Wiley, 1984. 

Quantum State Molecular Constants Reference Method 

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As the ENDOR spectrum is in effect an NMR spectrum obtained by devious means, when considering the response of a nucleus with spin / one must keep track of all interactions that it and its coupled electron spin undergo. The energy levels of an unpaired electronic spin S in an externally applied magnetic field, and the associated EPR spectra, are described in detail elsewhere in this volume. As described therein, the interaction of an electronic spin in an external magnetic field is characterized by the parameter g. In a molecule, the magnitude of the electron spin interaction depends on the orientation of the molecule with respect to the external magnetic field, and thus g is a tensor quantity. 

The magnetic properties of free radicals are represented by the parameters describing their interaction with external magnetic fields and the parameters of intramolecular hyperfine interactions. For many free radicals, in particular 5-atoms and radicals in liquid or solid environments where the orbital and rotational components of angular momentum are quenched, the parameters are conveniently given by the elements of the tensors g and of the spin-Hamiltonian... 

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