Hyperfine separation

The photodecomposition of isopropyl alcohol on silica gel produces a seven-line spectrum having a hyperfine separation of 20.7 G and an amplitude ratio of 1 6.7 20.2 31 21.1 7.4 1.5 (68). This spectrum was attributed to SiOCMe2 formed from the ether surface groups. In addition to this spectrum the spectrum of the methyl radical was also observed. Irradiation of adsorbed tert-butyl alcohol produced a three-line spectrum which was attributed to SiOMe2OCH2 (68). Apparently the splitting from the methyl protons was too small to be observed. 

Detailed calculations give the spin densities on the a, 0 and 02 carbon atoms as 0.622, —0.231 and 0.622 respectively. The hyperfine separation is given by... 

Experimental data on the hyperfine separations thus give values of the coupling constants, from which the corresponding nuclear moments magnetic dpole moment n, and spectroscopic electric quadrupole moment Q 2, may be evaluated. 

The hyperfine separations and the hyperfine structure constants determined much more accurately either... 

Hyperfine separations in hydrogen and its isotopes. In one of the first applications of the atomic hydrogen maser the hyperfine separations of hydrogen and its isotopes were remeasured to greatly increased accuracy. The results obtained were as follows ... 

The measurement in the case of hydrogen is based on the international definition of the second in terms of the hyperfine separation in atomic cesium, as discussed in section 18.7, while the results for deuterium and tritium are measured in terms of the hydrogen hyperfine frequency. From equations (18.36) and (18.42) the hyperfine separation for the hydrogen atom is given theoretically by... 

Show that the zero-field hyperfine separations deduced from these figures are 461-75 MHz and 803-54 MHz for and Li respectively and that the magnetic fields employed were 0-05 G and 0 15 G. 

Hyperfine stmcture measurements of 75 strong lines at 4020—6200 mm were made by means of interferometer spectrograms. Doublet stmctures occurred in 30 lines with separations of 0.034—0.180 cm ( )- Nuclear spins for Pu and for Pu have been estabUshed to be / = 1/2 and 1 = 5/2, respectively. The spins were based on paramagnetic resonance measurements on a RbPu02(N02)3 crystal (77). 

The origin of postulate (iii) lies in the electron-nuclear hyperfine interaction. If the energy separation between the T and S states of the radical pair is of the same order of magnitude as then the hyperfine interaction can represent a driving force for T-S mixing and this depends on the nuclear spin state. Only a relatively small preference for one spin-state compared with the other is necessary in the T-S mixing process in order to overcome the Boltzmann polarization (1 in 10 ). The effect is to make n.m.r. spectroscopy a much more sensitive technique in systems displaying CIDNP than in systems where only Boltzmann distributions of nuclear spin states obtain. More detailed consideration of postulate (iii) is deferred until Section II,D. 

In Fig. 4, nucleus is coupled to the electron on R and nucleus Hj is coupled to the electron on R by the hyperfine terms and Oj, respectively. The inter-radical separation is denoted by X, and J e is the electron exchange integral. The two radicals move relative to each other and, as shown above, this changes the values of Jee-... 

Most Mossbauer spectra are split because of the hyperfine interaction of the absorber (or source) nuclei with their electron shell and chemical environment which lifts the degeneracy of the nuclear states. If the hyperfine interaction is static with respect to the nuclear lifetime, the Mossbauer spectrum is a superposition of separate lines (i), according to the number of possible transitions. Each line has its own effective thickness t i), which is a fraction of the total thickness, determined by the relative intensity W of the lines, such that t i) = Wit. 

For the hydrogen atom, two such resonance conditions occur, giving rise to two lines separated by 506 G, which is just the value of a for the hydrogen atom [Eq. (ID)]. The spectrum would look the same for a single crystal or for a polycrystalline sample because the g factor and the hyperfine constant are isotropic. 

At either frequency the sensitivity of the instrument is quite remarkable. The exact signal-to-noise ratio depends upon a number of factors including apparent line width (including g and hyperfine anisotropy), ease of saturation, the temperature, and the linear density of the sample in the quartz tube. For a relatively narrow line with peak-to-peak separation of two gauss it is possible to observe the spectrum for concentrations as low as 1014 spins per gram of sample. As the spectrum becomes more anisotropic, the sensitivity of course decreases. Lowering the temperature increases the sensitivity since the population difference An increases [(Eqs. (26) and (3°)]. 

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