Hyperfine interaction structure

Ayy = (6.0 5.5) T, and A22 = (16.9 2.5) T (conventional dashed Unes). This again demonstrates the sensitivity of NFS for hyperfine interactions in nuclear ( Fe) scatterers. There can be no doubt that NFS benefits from experimental conditions such as polarization and time structure, and also from a beam diameter in the submillimeter range of the probing radiation. 

A fairly detailed treatment of the theory for hyperfine interactions has been given in Appendix D, and it is our intention to show how the results of this development can be used to determine molecular structure. Perhaps the most straightforward way to introduce the subject is to examine the experimental results for the NO2 molecule adsorbed on MgO (29). This molecule has been extensively studied in the gas, liquid, and solid phase, so that there is ample data for comparison purposes. 

The state of the superoxide ion has been summarized by Naceache et al. 22). It appears probable that an ionic model is most suitable for the adsorbed species since the hyperfine interaction with the adjacent cation is relatively small. Furthermore, the equivalent 170 hyperfine interaction suggests that the ion is adsorbed with its internuclear axis parallel to the plane of the surface and perpendicular to the axis of symmetry of the adsorption site. Hence, the covalent structures suggested by several investigators have not been verified by ESR data. 

FIGURE 10.4 Anisotropy averaging in the EPR of TEMPO as a function of temperature. The spectra are from a solution of 1 mM TEMPO in water/glycerol (10/90). The blow-up of the middle 14N (/ = 1) hyperfine line in the 90°C spectrum has been separately recorded on a more dilute sample (100 pM) to minimize dipolar broadening and, using a reduced modulation amplitude of 0.05 gauss, to minimize overmodulation. The multiline structure results from hyperfine interaction with several protons. 

Computer simulation of the experimental spectra in the frozen solution points to a spin-localized structure independent of the temperature. This interpretation is unambiguous because, in the solid state, the dipolar contributions of the hyperfine interaction A(dip) for all three principal... 

In summary, NMR techniques based upon chemical shifts and dipolar or scalar couplings of spin-1/2 nuclei can provide structural information about bonding environments in semiconductor alloys, and more specifically the extent to which substitutions are completely random, partially or fully-ordered, or even bimodal. Semiconductor alloys containing magnetic ions, typically transition metal ions, have also been studied by spin-1/2 NMR here the often-large frequency shifts are due to the electron hyperfine interaction, and so examples of such studies will be discussed in Sect. 3.5. For alloys containing only quadrupolar nuclei as NMR probes, such as many of the III-V compounds, the nuclear quadrupole interaction will play an important and often dominant role, and can be used to investigate alloy disorder (Sect. 3.8). 

The electron hyperfine interaction thus has important effects on both NMR relaxation and frequency shifts, and can provide valuable information on the incorporation of magnetic ions into semiconductor lattices and the resulting electronic structure as characterized by transferred hyperfine constants. Examples in Sect. 4 will show how the possible incorporation of magnetic ions into semiconductor nanoparticles can be studied by NMR. 

Hyperfine coupling constant, 22 267, 269 Hyperfine interaction, ESR data for, 22 274 Hyperfine parameters for O, 32 128-130 Hyperfine splitting, 31 81 Hyperfine structure, trimer species, 31 98-99 Hyperfine tensor, 22 267, 273-279, 336, 340 constants, 32 20-21 dioxygen species, 32 18-25 equivalent oxygen nuclei, 32 18-21 ionic oxides, 32 40... 

In contrast to the narrow signal of H(I), which exhibits a single Lorentzian profile, the feature observed for H(IV) and H(V) was more complex (Fig. 23 lb) with splitting into five lines indicating a superhyperfine structure (line denoted A in Fig. 23 2). This phenomenon is due to the hyperfine interaction between localized spin and two neighboring nitrogen nuclei (nuclear spin... 

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