Magnetic interactions between electrons

Magnetic interactions between electrons (the Breit interaction) can be treated perturbatively their effect on PNC is treated in Section 4.5.1. While in the previous section we chose U(r) to be one of a number of local potentials, for PNC we instead choose the Hartree-Fock potential, defined... 

Electrophosphorescence results from triplet emission in excitonic states activated by strong SOC. The strong SOC requires heavy-metal complex structures to increase the internal magnetic interaction between electron spins and orbital magnetic field. It is noted that the use of heavy-metal complex... 

The Mott cross-section is just the cross-section for the scattering of a spin 5 particle in the Coulomb field of a massive (spinless) target. The extra factors in (15.1.19) arise (i) because the target has spin 5 and there is a contribution due to the magnetic interaction between electron and muon, and (ii) because the target has finite mass and recoils. 

We will use here the main results obtained for two complex and distinct situations the structural and spectroscopic information gathered for D. gigas [NiFe] hydrogenase and AOR, in order to discuss relevant aspects related to magnetic interaction between the redox centers, intramolecular electron transfer, and, finally, interaction with other redox partners in direct relation with intermolecular electron transfer and processing of substrates to products. 

Foumel, A., Gambarelli, S., Guigliarelli, B., More, C., Asso, M., Chouteau, G., Hille, R., and Bertrand, P. 1998. Magnetic interactions between a 4Fe-4S l+ cluster and a flavin mononucleotide radical in the enzyme trimethylamine dehydrogenase a high-field electron paramagnetic resonance study. Journal of Chemical Physics 109 10905-10913. 

In the case of iron, magnetism is due to the unpaired electrons in the 3d-orbitals, which have all parallel spin. These electrons interact with all other electrons of the atom, also the s-electrons that have overlap with the nucleus. As the interaction between electrons with parallel spins is slightly less repulsive than between electrons with anti parallel spins, the s-electron cloud is polarized, which causes the large but also highly localized magnetic field at the nucleus. The field of any externally applied magnet adds vectorially to the internal magnetic field at the nucleus. 

In order to understand the nature of mixed-valent compounds one must consider both electrostatic and magnetic interactions between centres which have different oxidation states. Nevertheless, as schematically shown in Figure 14, simple electrostatic effects can help to clarify the so-called Robin-Day classification.24 This is based on the degree of electronic delocalization in (usually binuclear) mixed-valent compounds. 

Electron-nuclear double resonance (ENDOR) spectroscopy A magnetic resonance spectroscopic technique for the determination of hyperfine interactions between electrons and nuclear spins. There are two principal techniques. In continuous-wave ENDOR the intensity of an electron paramagnetic resonance signal, partially saturated with microwave power, is measured as radio frequency is applied. In pulsed ENDOR the radio frequency is applied as pulses and the EPR signal is detected as a spin-echo. In each case an enhancement of the EPR signal is observed when the radiofrequency is in resonance with the coupled nuclei. 

For a quasi-relativistic framework as relevant to chemistry (21), we may neglect the magnetic retardation between the electrons and the nuclei and therefore employ standard Coulombic interaction operators for the electrostatic interaction. The interaction between the electrons and the nuclei is not specified explicitly but we only describe the interactions by some external 4-potential. For the sake of brevity this 4-potential shall comprise all external contributions. Explicit expressions for the interaction between electrons and nuclei will be introduced at a later stage. Furthermore, we can neglect the relativistic nature of the kinetic energy of the nuclei and employ the non-relativistic kinetic energy operator denoted as hnuc(I),... 

These fields become important in magnetic resonance spectroscopies, where the interaction between electronic and nuclear spins is considered in phenomenological Spin Hamiltonians. Note... 

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