Nuclear spin levels

Translational levels are too closely spaced to be considered quantized, while the very small differences between nuclear spin levels arise only when the molecules are subjected to a strong magnetic field. 

Nuclear relaxation rates, iron-sulfur proteins, 47 267-268 Nuclear resonance boron hydrides and, 1 131-138 fluorescence, 6 438-445 Nuclear spin levels, 13 140-145 Magnetic properties of nuclei, 13 141-145 Nuclear testing... 

The theory of CIDNP depends on the nuclear spin dependence of intersystem crossing in a radical (ion) pair, and the electron spin dependence of radical pair reaction rates. These principles cause a sorting of nuclear spin states into different products, resulting in characteristic nonequilibrium populations in the nuclear spin levels of geminate (in cage) reaction products, and complementary populations in free radical (escape) products. The effects are optimal for radical parrs with nanosecond lifetimes. 

Symmetries of local electrical environments of quadrupolar nuclei (/ 1) profoundly influence relaxation times and resonance line shapes of such nuclei (9, 116). Consider a nucleus for which I = % (Br79, Bn). In the absence of quadrupolar perturbation, the nuclear spin levels are evenly spaced, as shown in I below, and the three possible nuclear resonance transitions have equal energies (Am = 1). If, however, eqQ 0... 

Nuclear magnetic resonance (NMR) 10 2-10-4 Transitions between nuclear spin levels in magnetic fields... 

Earlier in this chapter when dealing with the nuclear Zeeman interaction we calculated the behaviour of the nuclear spin levels of H2 ignoring the effects of nuclear shielding. We now return to this question in more detail. We have shown that the Zeeman interaction for a nucleus of spin I should be written in the form... 

This might not be the case if the spin-orbit coupling in these molecules involves the orbital motion of the electron and the total spin angular momentum of the electron and nuclear spins. In this case, the intersystem crossing process might also be different for different nuclear spin levels belonging to the same electron-spin level. 

Okazaki et al. showed some examples for spin-manipulation [14] (1) Because the yield of spin adducts produced from escape radicals was found to be decreased by the resonance microwave irradiation, the yield of cage (escape) products was found to be increased (decreased) with a high pressure liquid chromatography (HPLC) technique. (2) Because the resonance microwave irradiation induces a transition between two definite nuclear spin-levels, the enrichment of this nuclear spin could be realized. Indeed, the ratio of was... 

Molecular beam resonance can be performed in a magnetic field or an electric field. In molecular beam magnetic resonance, when the Zee-man interaction is much larger than the quadrupole interaction, as it is for deuterium in a high magnetic field, transitions between nuclear spin levels are detected with splittings caused by quadrupole interactions. 

Sampling the polarizations created by the CIDNP effect with a continuous wave NMR spectrometer is straightforward because with that detection scheme the line intensity of a transition L(r5) between nuclear spin levels r and s is proportional to the population difference (Pr — Ps) of these levels only. However, with pulsed detection, as is now universally employed, L(rs) depends on the population differences across all parallel transitions between levels t and u including the one between r and s, and also in a complicated manner on the tip angle 9 of the observation pulse. For a weakly coupled system of N spins, one has [37]... 

Thus, in the recombination product the p nuclear spin level, which is higher in energy, is overpopulated. This leads to an emissive NMR sigrutl for this product. 

The Pr ground state nuclear spin levels consist of three levels split by the second-order hyperfine interaction and the relatively small nuclear electric quadrupole interaction. In non-zero magnetic fields each of these levels is additionally split due to the enhanced Zeeman interaction (see Fig. 4), The Hamiltonian of this system has been given by Teplov. ... 

Radio frequency 3 X 10 - 9 X 10 Nuclear magnetic resonance Nuclear spin levels... 

The translational motions and spin dynamics of conduction electrons in metals produce fluctuating local magnetic hyperfine fields. These couple to the nuclear magnetic moments, inducing transitions between nuclear spin levels and causing nuclear spin relaxation. The translational motions of electrons occur on a very rapid time scale in metals (<10 s), so the frequency spectrum of hyperfine field fluctuations is spread over a wide range of w-values. Only a small fraction of the spectral intensity falls at the relatively low nuclear resonance frequency (ojq 10 s ). Nevertheless, the interaction is so strong that this process is usually the dominant mode of relaxation for nuclei in metallic systems, either solid or liquid. 

The technique of LMR is very similar to other magnetic resonance methods such as EPR and NMR. While NMR uses radiofrequency radiation to produce transitions between nuclear spin levels, and EPR uses microwave radiation to produce transitions between electron spin levels, LMR uses... 

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