Angular momentum magnetic spectra

Two kinds of environmental interactions are commonly important in the ESR spectrum of a free radical (i) To the extent that the unpaired electron has residual, or unquenched, orbital angular momentum, the total magnetic moment is different from the spin-only moment (either larger or smaller,... 

In our discussion of the far-infrared laser magnetic resonance spectrum of NiH in chapter 9, a fairly general effective Hamiltonian was presented. This Hamiltonian included terms which would produce A-doubling in a A state, an unusual situation because one requires electronic orbital angular momentum operators to connect A = + 2 and A = - 2 components [77], The effective Hamiltonian used to analyse the mi-crowave/optical double resonance spectrum of NiH was as follows ... 

For the total angular momentum would then be j, and the total magnetic moment would be = (eA/47T/xc) thus j and Mj would have the same direction, and would set themselves in the magnetic field in accordance with the quantisation of direction, or process round the field direction in common. The single difference, with spin, would be that now, not + 1, but 2j + 1 setting possibilities exist, and that therefore every undisturbed term is split up by the magnetic field into 2j + 1 terms, but in such a way that the amount of the splitting would be exactly the same as before in the spectrum there would be no difference at all. 

There are many sources that contribute to an ESR spectrum. Apart from the applied external field, local magnetic fields are also created within the sample by other unpaired electrons in the molecule or the surroundings, or from magnetic nuclei in the molecule/ion. There may also be contributions to the hf structure arising from the orbital angular momentum of the electron, which will influence the electronic g-value. In the present calculations, the g-value of the free electron, g = 2.0023, is assumed throughout. 

---