First-order perturbation nuclear magnetic resonance

Electron spin resonance spectroscopy is formally similar to NMR if one considers an unpaired electron as taking the role of a spin -1/2 nucleus in an NMR experiment. However, because of the much greater size of the electron magneton (the Bohr magneton) versus the nuclear magneton, much weaker external fields are employed in order to observe transitions with radiofrequency radiation. As a result, coupling interactions between the electron and magnetic nuclei may require a treatment beyond that of first-order perturbation theory. 

We calculate the effects of the Hamiltonian (8.105) on these zeroth-order states using perturbation theory. This is exactly the same procedure as that which we used to construct the effective Hamiltonian in chapter 7. Our objective here is to formulate the terms in the effective Hamiltonian which describe the nuclear spin-rotation interaction and the susceptibility and chemical shift terms in the Zeeman Hamiltonian. We deal with them in much more detail at this point so that we can interpret the measurements on closed shell molecules by molecular beam magnetic resonance. The first-order corrections of the perturbation Hamiltonian are readily calculated to be... 

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