Hyperfine splitting factors

Figure 24. Hyperfine splitting factors of 6sns Sj Rydberg states of Ba. (Taken from Ref, 55.)...

Comparing Eqs. (53)-(56) with the usual expression for the hyperfine components Ep in terms of the hyperfine splitting factor A... 

Figure 37. Hyperfine splitting factor A of Asnd D2 Rydberg states of Ca. The solid line connecting the data has been drawn to guide the eye. (Taken from Ref. 42.)...

In Figures 37-39, the hyperfine splitting factors ACD2) of msnd D2 Rydberg series of and have been plotted versus... 

Fig. 14. Hyperfine splitting factor of the 4snd Ca-43 (part a) and separation of 4snd (part b) as a function of n.

A second type of structural information can be deduced from the hyperfine splitting in EPR spectra. The origin of this splitting is closely related to the factors that cause spin-spin splitting in proton NMR spectra. Certain nuclei have a magnetic moment. Those which are of particular interest in organic chemistry include H, " N, F, and P. 

The information that can be obtained from an epr spectrum can be divided into three forms (i) the 0-factor, (ii) the hyperfine splitting of the spectra due to the interaction of the spin with magnetic nuclei in the radical and (iii) the shape of the observed bands. 

EPR spectroscopy is the most important method for determining the structures of transient radicals. Information obtained from the EPR spectra of organic radicals in solution are (i) the centre position of the spectra associated with g factors, (ii) the number and spacing of the spectral lines related to hyperfine splitting (hfs) constants, (iii) the total absorption intensity which corresponds to the radical concentration, and (iv) the line widths which can offer kinetic information such as rotational or conformational barriers. The basic principles as well as extensive treatments of EPR spectroscopy have been described in a number of books and reviews and the reader is referred to this literature for a general discussion [28 30]. 

Radical anions derived from 2,5-diformylthieno[3,2-6]thiophene (39) as well as (40) were studied in connection with the conformational analysis of heteroaromatic carbonyl compounds. Different ESR signals were given by distinct rotational isomers. Information on interconversion of the rotamers could not be obtained since the radicals were unstable at the temperatures necessary for interconversion. On the other hand, ketyl radicals derived from ketones (41) and (42) are relatively more stable at the temperatures needed for the study of the conformational mobility in these systems. The ESR spectra of the bis-thienothienyl ketyls from (41) and (42) at room temperature show that the unpaired electron is coupled to three pairs of equivalent protons. Both spectra exhibited a certain amount of asymmetry, which was enhanced by lowering the temperature. At -10°C the highfield part of the spectra split into new lines arising from two species which have similar hyperfine splitting, but different g factors. These have been identified as the rotational isomers of the radicals. The two preferred conformations are cis-trans and trans-trans. An examination... 

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