Fermi contact hyperfine field

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. 

Although attempts have been made to correlate the hyperfine field of a mixed-valence compound with the weighted mean of the Fermi contact-interaction field H, = 220 < Sz > kOe , the orbital and spin-moment contributions Hl and Hd, which may be comparable to H, at Fe(II) ions, make any such correlations dubious ... 

In addition to the isomer shift and the quadrupole splitting, it is possible to obtain the hyperfine coupling tensor from a Mossbauer experiment if a magnetic field is applied. This additional parameter describes the interactions between impaired electrons and the nuclear magnetic moment. Three terms contribute to the hyperfine coupling (i) the isotropic Fermi contact, (ii) the spin—dipole... 

Barone and coworkers250 also determined EPR hyperfine splittings nN of the radical 40 at the UMP2/DZ + P level of theory using the Fermi contact operator and a finite field method with an increment size of 0.001 a.u. Expectation values of aN, < aN >, at higher temperatures T were calculated by assuming a Boltzmann population of vibrational levels according to equation 23 ... 

The coupling tensor (P) to the paramagnetic ion produces two main sources of additional field. One is the Fermi contact or hyperfine interaction. The general form of the contact interaction produces a Hamiltonian... 

The Contact (or Fermi) component Hc of the magnetic hyperfine field at the Fe nucleus may be expected to be by far the largest in the present compound. Hc is proportional to the spin density at the Fe nucleus... 

Within a nonrelativistic calculation of the hyperfine fields in cubic solids, one gets only contributions from s electrons via the Fermi contact interaction. Accounting for the spin-orbit coupling, however, leads to contributions from non-s elections as well. On the basis of the results for the orbital magnetic moments we may expect that these are primarily due to the orbital hyperfine interaction. Nevertheless, there might be a contribution via the spin-dipolar interaction as well. A most detailed investigation of this issue is achieved by using the proper relativistic expressions for the Fermi-contact (F), spin-dipolar (dip) and orbital (oib) hyperfine interaction operators (Battocletti... 

Millimeter wave spectroscopy with a free space cell such as a Broida oven is more sensitive than lower frequency microwave spectroscopy. However, the higher J transitions monitored by millimeter wave spectroscopy often do not show the effects of hyperfine structure. In the case of CaOH and SrOH, the proton hyperfine structure was measured in beautiful pump-probe microwave optical double resonance experiments in the Steimle group [24,68], They adapted the classic atomic beam magnetic resonance experiments to work with a pulsed laser vaporization source and replaced the microwave fields in the A and C regions by optical fields (Fig. 15). These sensitive, high-precision measurements yielded a very small value for the proton Fermi contact parameter (bF), consistent with ionic bonding and a... 

The nuclear hyperfine coupling is the field at the electron due to the nucleus and its magnitude depends on whether the electron which is interacting with the nucleus is in an s or a p or orbital. Since s orbitals have high electron density at the nucleus, the hyperfine coupling constant will be large and since s orbitals are symmetrical, it will be independent of direction. This interaction is called the isotropic hyperfine coupling (Aijo) or the Fermi contact interaction. In p or d orbitals, where there... 

Analogously, the Fermi contact and dipolar hyperfine interaction terms originate in the interaction between the electronic magnetic moment and the internal magnetic field generated by the nucleus... 

Let us start with the field-free SO effects. Perturbation by SO coupling mixes some triplet character into the formally closed-shell ground-state wavefunction. Therefore, electronic spin has to be dealt with as a further degree of freedom. This leads to hyperfine interactions between electronic and nuclear spins, in a BP framework expressed as Fermi-contact (FC) and spin-dipolar (SD) terms (in other quasirelativistic frameworks, the hyperfine terms may be contained in a single operator, see e.g. [34,40,39]). Thus, in addition to the first-order and second-order ct at the nonrelativistic level (eqs. 5-7), third-order contributions to nuclear shielding (8) arise, that couple the one- and two-electron SO operators (9) and (10) to the FC and SD Hamiltonians (11) and (12), respectively. Throughout this article, we will follow the notation introduced in [58,61,62], where these spin-orbit shielding contributions were denoted... 

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