Hyperfme interaction

The interaction of the electron spin s magnetic dipole moment with the magnetic dipole moments of nearby nuclear spins provides another contribution to the state energies and the number of energy levels, between which transitions may occur. This gives rise to the hyperfme structure in the EPR spectrum. The so-called hyperfme interaction (HFI) is described by the Hamiltonian... 

The simplest system exliibiting a nuclear hyperfme interaction is the hydrogen atom with a coupling constant of 1420 MHz. If different isotopes of the same element exhibit hyperfme couplings, their ratio is detemiined by the ratio of the nuclear g-values. Small deviations from this ratio may occur for the Femii contact interaction, since the electron spin probes the inner stmcture of the nucleus if it is in an s orbital. However, this so-called hyperfme anomaly is usually smaller than 1 %. 

Even for a single radical tire spectral resolution can be enlianced for disordered solid samples if the inliomogeneous linewidth is dominated by iimesolved hyperfme interactions. Whereas the hyperfme line broadening is not field dependent, tire anisotropic g-matrix contribution scales linearly with the external field. Thus, if the magnetic field is large enough, i.e. when the condition... 

Figure Bl.16.5. An example of the CIDNP net effect for a radical pair with one hyperfme interaction. Initial conditions g > g2, negative and the RP is initially singlet. Polarized nuclear spin states and schematic NMR spectra are shown for the recombination and scavenging products in the boxes.

Figure Bl.16.8. Example of CIDNP multiplet effect for a syimnetric radical pair with two hyperfme interactions on each radical. Part A is the radical pair. Part B shows the spin levels with relative Q values indicated on each level. Part C shows the spm levels with relative populations indicated by the thickness of each level and the schematic NMR spectrum of the recombination product.

Bauer, Ph. Genin, J.M. Rezel, D. (1986) Mossbauer effect evidence of chlorine environments in ferric oxyhydroxides from iron corrosion in chlorinated aqueous solution. Hyperfme Interactions 28 757-760... 

Bowen, L.H. De Grave, E. Bryan, A.M. (1994) Mossbauer studies in external field of well-crystallized Al-maghemites made from hematite. Hyperfme Interactions 94 1977-1982... 

Coey, J.M.D. Sawatzky, G.A. (1971) A study of hyperfme interactions in the system (Fei xRhj203 using the Mossbauer effect. J. Phys. C4 2383... 

Dang, M.-Z. Rancourt, D.G. Dutrizac J.E. La-marche, G. Provencher, R. (1998) Interplay of surface conditions, particle size, stoichiometry, cell parameters, and magnetism in synthetic hematite-like materials. Hyperfme Interactions 117 271-319 Daniele, P.G. Rigano, C. Sammartano, S. Zeland,V. (1994) Ionic strength dependence of formation constants - XVIII. The hydrolysis of iron(III) in aqueous KNOj solutions.Ta-lanta41 1577-1582... 

Tfonc, E. Chaneac, C. Jolivet, J.P. (1998) Structural and magnetic characterzation of -Pe203. J. Solid State Chem. 139 93-104 Tfonc, E. Jolivet, J.P. Livage, J. (1990) Mdss-bauer investigation of the -a-Fe203 transformation in small particles. Hyperfme Interactions 54 737-740... 

Mossbauer characterization of iron oxides and (oxy)hydroxides the present state of the art. Hyperfme Interactions 126 247-259... 

E. Stiers,W. (1986) Fe Mossbauer effect study of Mn-substituted goethite and hematite. Hyperfme Interactions 29 1157-1160... 

For the magnetic hyperfme interaction we deal with the three terms separately, expanding each in the space-fixed axis system, as follows ... 

Finally, the matrix elements of the fluorine dipolar hyperfme interaction (equation (10.76)) are given by... 

The values of the g-factor (gy = 1.9951 and gi = 1.9956), hyperfme interaction constants, and the electron wave function for FA-centers in ZnO correlate well with similar parameters for the Fa- and F -centers in CaO and ZnS. Here, Liz seems to be the impurity in the FA-center in the crystals we have investigated. This assumption is based on the fact that the investigated hydrothermal single crystals were doped with lithium with a concentration of Nli s lO cm during the process of growing. The unpaired electron of the FA-center interacts with the impurity having nuclear spin J = 3/2, which is also well satisfied for lithium, which in the natural state contains 92.58% of the isotope Li with J = 3/2. 

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