Hyperfine spectra

Sevilla et The analysis of the hyperfine spectra of these radicals has revealed that the cation radical should have D2H symmetry, whereas the molecular symmetry of the anion radical should be lower than the apparently-full molecular symmetry, i. e., We now examine the molecular symmetries of the anion and cation radicals of heptafulvalene, together with those of its 5-membered analogue, fulvalene PCXI) using the symmetry rule. 

The anisotropic/factor may also manifest itself in the relative line intensities of Zeeman split hyperfine spectra in a poly crystalline absorber. Expanding f(0) in a power series... 

Other factors to be considered by the experimentalist are that the high spins (5/2 and 7/2 ) of the nuclear states involved cause the hyperfine spectra to consist of many components (eight for quadrupole splitting and 18 for magnetic splitting). Therefore, large electric field... 

When gf3eHspaced lines is to be expected only when the spectrometer frequency is large enough to require gfieH >A. For large hyperfine interactions or low spectrometer frequencies, the spectrum can deviate greatly from the simple pattern observed at high frequencies. 

Figure 11.56. Block diagram of the ion quadrupole trap apparatus used to detect magnetic resonance and hyperfine spectra of the Hj ion [108].

Based on this model, the hyperfine spectra for the defect can be related to the s- and p- components of the wavefunction (Stutzmann and Biegelsen, 1988). Table 4.1 shows the results and compares them with the silicon defects which are known to be of the dangling bond type in other materials. An sp dangling bond has J s-like and p-like character, so should have a = 0.5 and p = 0.87. In practice, all the defects in Table 4.1 have a slightly smaller s-character and larger p-character and also incomplete localization, compared to the sp dangling bond model. 

FIGURE 15 The first ESR hyperfine spectra (9.112 GHz) of La Cgj at room temperature of (A) solid degassed toluene extract and (B) a degassed solution of the dried extract in 1,1,2,2-tetrachloroethane. 

Interaction between the magnetic field of the electrons and the nuclear spin is the basis for various techniques that are broadly applied in chemistry, atomic physics, nuclear physics and solid-state physics. The magnetic field of the electrons is due to their spin and orbital angular momentum and much larger than the magnetic field of the nucleus. Consequently, the nuclear spin is oriented in relation to the field produced by the electron shell. This leads to hyperfine spectra which can be resolved by means of optical spectrometers of very high resolution. 

Analysis of Magnetic Hyperfine Spectra 2.1 Diamagnetic Heme Proteins... 

Fig. 31. 57Fe Mossbauer spectra of Tm2Fe14B at 318 K (upper curve) and 294 K (lower curve). The solid curves are fits by six magnetic hyperfine spectra with relative intensities in the ratios 16 16 8 8 4 4. The positions and relative intensities of the peaks of these subspectra are shown by the corresponding bar...

Only two of the naturally occurring isotopes of titanium have nonzero nuclear spin Ti with / = f (7.75%) and Ti with / = f (5.51%). Hyperfine spectra in solution will thus consist of a strong central line I = 0) flanked by a sextet (/ = f) and an octet (7 = f) state superimposed on each other since is nearly the same for both nuclei. The spectrum will thus consist of a series of lines of approximate relative intensities 1 3 3 3 120 3 3 3 1. A typical spectrum is shown in Fig. 

ESR studies of copper(2 + ) doped barium sulphamate (12) single crystals show well-resolved hyperfine spectra of 63Cu superimposed with superhyperfine lines due to 14N nuclei33. 

It will be obvious that there are close similarities between the ordered magnetic and disordered paramagnetic hyperfine spectra. The hyperfine fields originate in similar ways, and the angular properties of the transitions... 

Anisotropy effects have also been calculated to be detectable as an alteration of the intensity ratios in magnetic hyperfine spectra [61]. For quadrupole spectra with higher spin states it is sometimes possible to observe intensity discrepancies between the m = 0, m = 1, and the 1 -> ibi groups of transitions, each of which has different angular properties. Examples are to be found in I2 [62] and IBr, ICl [63] where vibrational anisotropy is assumed. 

Mossbauer hyperfine spectra are useful in the determination of nuclear parameters, especially those of the excited states. Their significance stems from the fact that the structure of the nucleus is still poorly understood. Comparison of the parameters as measured with the values estimated from theory is used to discover the validity or inadequacy of the nuclear model. The rare-earth elements are popular for this type of work because of the proliferation of Mossbauer resonances, making it feasible to study the effects of successive proton or neutron addition over a range of nuclei. Although theory and experiment are sometimes in accord, gross differences are not unusual. 

Iron alloys containing O-6 O at. % Mo show complex hyperfine spectra which can be analysed in terms of fields from iron atoms with 0, 1, and 2 Mo nearest neighbours [61, 62]. The decrease in field per Mo atom is unusually large at about 40 kG. FeaMo2 gives a simple quadrupole doublet at room temperature, and Fe2Mo has been identified as a precipitate in an alloy containing 20 at. % Mo [62]. 

This phenomenon is appropriate to the paramagnetic hyperfine spectra of magnetically dilute iron phases, and contrasts with the magnetically concentrated rare-earth paramagnetic hyperfine spectra where the effective-field approximation holds. However, it is possible to revert to the former situation by magnetic dilution. This has been shown in erbium ethyl sulphate diluted with the corresponding yttrium salt [138]. The hyperfine tensor was already known from e.s.r. data to be less anisotropic than usual, and the spec-... 

Fig. 17.27 Magnetic hyperfine spectra in thulium metal at various temperatures (in K) together with calculated spectra using a model in which the magnetic and crystal lattices are incommensurate. [Ref. 170, Fig. 2]...

The 1+ i— spin-states of the El transition result in a large number of hyperfine lines, and although the resonance linewidths are invariably broad, they have proved to be much less than the separations between hyperfine components in many cases. Typical hyperfine spectra are shown in Fig. 18.4. 

Vitko, Jr., J. 1978. ESR studies of hydrogen hyperfine spectra in irradiated vitreous silica. J. Appl. Phys. 49 5530-5535. 

Precision measurements of hyperfine structure and isotope shifts yield information on nuclear spins, quadrapole moments, and nuclear deformations. The results of these experiments allow tests of nuclear models of the spatial distribution of protons and neutrons in highly deformed nuclei [467]. In Fig. 4.8 the hyperfine spectra of different Na isotopes are depicted, which had been produced by spallation of aluminum nuclei by proton bombardment according to the reaction Al(/ , 3p,xn) Na [468] and in Fig. 4.29 the hfs of 6 isotopes of the titanium ion H+ illustrates the good signal-to-noise ratio. Such precision measurements have been performed in several laboratories for different families of isotopes [466-469]. 

Fig. 4.29 Hyperfine spectra of 6 isotopes of the Titan ions for the determination of nuclear spins, magnetic moments and isotope shifts [468]...

The nuclear spin quantum number of excited state can be derived from the hyperfine spectra, but this is usually known before the Mossbauer experiment. 

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