Transitions between the nuclear spin quantum states - NMR technique

7 TRANSITIONS BETWEEN THE NUCLEAR SPIN QUANTUM STATES - NMR TECHNIQUE 

The magnetic field that a particular nucleus feels differs from the external magnetic field applied, because the electronic structure in which the nucleus is immersed in, makes its own contribution (see Fig. 12.11.b,c). Also the nuclear spins interact by creating their own magnetic fields. 

We have notyet considered these effects in the non-relativistic Hamiltonian (2.1) (e.g., no spin-spin or spin-field interactions). The effects which we are now dealing with are so small, of the order of 10 kcal/mole, that they are of no importance for most applications, including UV-VIS, IR, Raman spectra, electronic structure, chemical reactions, intermolecular interactions, etc. This time, however, the situation changes we are going to study very subtle interactions using the NMR technique which aims precisely at the energy levels that result from spinnspin and spin-magnetic field interactions. Even if these effects are very small, they can be observed. Therefore, we have to consider more exact Hamiltonians. First, we have to introduce 

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Transitions between the nuclear spin quantum states - NMR technique... 

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