Fermi contact hyperfine

Here /, is the 13C nuclear spin, S is the unpaired electronic spin, and A j- is the Fermi contact hyperfine coupling tensor. This coupling is identical for all 13C nuclei as long as the C60 ion is spherical, but becomes different for different nuclei after the Jahn-Teller distortion leading to an inhomogeneous frequency distribution. The homogeneous width of the 13C NMR lines is, on the other hand, mainly determined by the electron-nuclear dipolar interaction... 

Using the full form of the Fermi contact hyperfine interaction given in equation (7.144), which differs from equation (7.287) in that it contains an explicit summation over the open shell electrons, we have that... 

The Fermi contact hyperfine interaction is written in the form... 

The inversion operation i which leads to the g/u classification of the electronic states is not a true symmetry operation because it does not commute with the Fermi contact hyperfine Hamiltonian. The operator i acts within the molecule-fixed axis system on electron orbital and vibrational coordinates only. It does not affect electron or nuclear spin coordinates and therefore cannot be used to classify the total wave function of the molecule. Since g and u are not exact labels, it was realised by Bunker and Moss [265] that electric dipole pure rotational transitions were possible in ll], the g/u symmetry breaking (and simultaneous ortho-para mixing) being relatively large for levels very close to the dissociation asymptote. The electric dipole transition moment for the 19,1 19,0 rotational transition in the ground electronic state was calculated... 

The 139La nucleus has a spin of 7/2 the Fermi contact hyperfine interaction is large in the B state and very large in the X state. Consequently the B -> A fluorescence spectrum exhibits a distinctive hyperfine structure, an example of which... 

The isotropic or Fermi contact hyperfine (hf) coupling constant ap was first obtained for both nuclei ip and from ESR spectra of ground-state PHg isolated at low temperature in rare-gas matrices (see the second table below). Anisotropic or dipolar features were first detected for 3 P with PHg anchored by H bonding in a frozen aqueous solution of sulfuric acid [1 ]. Complete sets of ap and the anisotropic components Tqq (q = inertial axes a, b, c XTqq=0) for both nuclei of ground-state PHg were later determined by far-IR laser magnetic resonance (FIR, LMR) [2] and microwave (MW) [3, 4] spectra. The latter [3, 4] also yielded data for the interaction constants Cqq(3ip). Interaction constants were also obtained for the electronically... 

The original work of Ruderman and Kittel is concerned with the interaction between nuclear spins due to the indirect interaction of the conduction electrons in simple s band metals. There the interaction between the electrons and the spins comes from the Fermi contact hyperfine interaction, so the matrix elements are independent of the initial and final wave vectors. The band structure is parabolic. If the same assumptions are made for the rare earths, the indirect coupling energy in eq. (3.56) has the form... 

The observed NMR shift, expressed as Am/materials containing 3 /-transition metals is proportional to the unpaired electron spin density at the nucleus site. The magnitude of the interaction is directly proportional to the Fermi constant Ac and the time-averaged electron spin (5z) by... 

Gas Phase. The isotropic or Fermi contact hyperfine (hf) coupling constant Ajgo and the anisotropic or dipole hf tensor elements Agg, A b, and A c of NH2 in the X Bi(0,0,0) and A Ai(0,V2,0) states are compiled in Table 9. The experimentally determined constants were derived from microwave optical double resonance (MODR), microwave absorption (MWA), laser magnetic resonance (LMR), infrared optical double resonance (lODR), optical optical double resonance (OODR), saturation, and magnetic level-crossing spectra. 

The portion of the isotropic nuclear resonance shift arising from the Fermi contact hyperfine interaction is called the contact contribution (as discussed in Chapter 2 Section 8.3). Contact shifts of a nucleus in a molecule with electron spin S and an axially symmetric g tensor are given by... 

The calculated Fermi contact hyperfine field, Bhf,c, calculated for 1 ML of Fe on W(llO) was decomposed into core-Bhfcp and conduction-Bhf,ce electron contributions. The core electrons contribute to Bhf.cp vvith a large negative value of — 30.6T, which scales exactly with the magnetic moment. The conduction electrons contribute to Bhf,ce with a positive value of 15.8 T (because of direct polarization) and greatly reduce the magnitude of the total Fermi contact term. 

---