From hyperfine interaction

A second type of defect is associated with boron or aluminum impurities that are present in SiCh- In porous glass Muha (129) observed a rather complex spectrum which results from hyperfine interaction with 10B and UB isotopes. The spectrum is characterized by g = 2.0100, g = 2.0023, an = 15 and a a. = 13 G for nB. The paramagnetic defect is apparently a hole trapped on an oxygen atom which is bonded to a trigonally coordinated boron atom. This center is irreversibly destroyed upon adsorption of hydrogen. 

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. 

As will be explained in Chapter 7, spectroscopic methods are a powerful way to probe the active sites of the hydrogenases. Often spectroscopic methods are greatly enhanced by judicious enrichment of the active sites with a stable isotope. For example, Mossbauer spectroscopy detects only the isotope Fe, which is present at only 2.2 per cent abundance in natural iron. Hydrogen atoms, which cannot be seen by X-ray diffraction for example, can be studied by EPR and ENDOR spectroscopy, which exploit the hyperfine interactions between the unpaired electron spin and nuclear spins. More detailed information has been derived from hyperfine interactions with nuclei such as Ni and Se, in the active sites. In FTTR spec-... 

A quartet is expected for this radical from hyperfine interaction with Cl86 and Cl37 nuclei, both of which have a spin of 3/2, and nearly equal magnetic moments. 

In addition to k values, force constants (Table 6) for the hydrogen bond bending have been calculated from root-mean square angles from hyperfine interactions, using a triatomic model ... 

Determination of Electron Distribution from Hyperfine Interaction... 

Fig. 3.41 A schematic representation of effects from hyperfine interactions in Mossbauer spectra . (Reprinted with permission from ref. 13. Copyright 1974 Pion Limited, London.)...

THz-TDS was also used to study the benchmark of molecular nanomagnetism, Mni2Ac [102-104], but has not been employed to study MNM since. These early studies demonstrated that the ZES of MNMs can be obtained by THz-TDS. Parks et al. then investigated the linewidth in some detail, where they considered contributions from hyperfine interactions and intermolecular magneto-dipolar interactions on the linewidth and concluded that, in addition to these, there must also be a distribution in the Z)-parameter. These investigations also made use of the fact that both amplitude and phase of the THz electric field are obtained, which can be converted to the real and imaginary parts of the index of refraction. 

In February 1971 the Bell labs and Rutgers group followed [22] with the manuscript Hyperfine Interactions and Geometry of Methylene. They estimated the %s character from hyperfine interaction and used %s versus angle data from Harrison [15] to fix angle at 137°. 

An analysis of the ESR spectra of PH4 (and deuterated species) in xenon and neopentane matrices confirmed the theoretically obtained TBP-eq structure of PH4 [1 to 3, 23]. The best resolved ESR spectrum of PH4 was observed In a neopentane matrix [2]. The spectrum at 100 K consists of eight 0.6 mT triplets (1 2 1). The large Interaction of -50 mT was due to a P nucleus, and the smaller (-0.6 and 20 mT) interactions were due to pairs of equivalent protons. The ESR spectrum of PD4 In neopentane-di2 consisted of a pair of 3 mT quintets (1 2 3 2 1) arising from hyperfine interactions with a 3i p nucleus and two equivalent deuter-ons [3]. Anisotropic features in the spectrum of PH4 in a xenon matrix at 4.2 K were Interpreted in terms of fast torsional oscillations about the symmetry axis of PH4 [2]. The following g fac-... 

Figure 7.7 Arrhenius plot of reciprocal correlation times extracted from the longitudinal muon spin relaxation measurements of benzene chromium tricarbonyl compared with QENS data [4]. Reproduced from Hyperfine Interactions 106, 27-32 (1997), U. A. Jayasooriya, I A. Stride, G. M. Aston, G. A. Hopkins, S. F. J. Cox, S. P. Cottrell and C. A. Scott, Figure 2, Kluwer, with kind permission of Kluwer Academic Publishers.

Magnetic structure determinations In certain cases details of the magnetic structure can be elucidated from hyperfine interaction measurements. For example, in Mbssbauer effect experiments employing single crystal absorbers, the relative intensities of the component lines of the spectrum depend on the angle between the gamma ray quantum and the hyperfine field at the nucleus. The latter is in turn parallel to the ionic moment. By such an experiment, Reese and... 

Dikanov SA, Shubin AA, Parmon VN. 1981. Modulation effects in the electron spin echo resulting from hyperfine interaction with a nucleus of an arbitrary spin. J Magn Reson 42 474-487. 

Although proton hyperfine interactions are by far the most common in aromatic radicals, a great deal of information about spin densities can also be derived from hyperfine interactions with and so forth. 

FIGURE 7. The ESR spectrum of the electrogenerated radical anion of 2-nitropropane, (CH3)2CHN02, in aqueous solution, showing a triplet of doublets. The former arise from hyperfine interaction with and the latter with... 

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