the Overhauser effect/method was posposed by Albert W. Overhauser on 1953, that, it can polarizing nuclei. or later called Dynamic Nuclear polarization.

the spin Hamiltonian is

where S is the electron spin, I is nuclear spin, B is external field strength and A is hyperfine structure coupling tensor. is a constant such that:

it related to the Larmor (angular ) frequency, which is in radius by :

it is same for proton with a corresponding g-factor and mass, or other nuclei with g-factor and charge and mass. for example, proton Larmor frequency is:

the Hamiltonian commute for both spin eigenstate. thus, we can write the energy as:

where m is the eigenvalue of and M is the eigenvalue for . For spin-half electron and nuclei, there will be 4 levels by . the selection rule is:

this is called the Overhauser Effect.

The Jeffries-Abragam Effect occur when a pumping radiation induced a “forbidden” transition”:

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