Hydrogen nuclei hyperfine coupling constants

Table 3.26 shows the results of ab initio calculations of the CH3 hyperfine coupling constants. The correct qualitative results are obtained—a positive spin density at the carbon nucleus and a negative spin density at the hydrogen nuclei. The magnitudes of the spin densities are too large, however. They... 

Consider an unpaired electron on a hydrogen atom, which has a nuclear spin I =. The nucleus (a single proton) has two possible orientations of its spin, labeled by ntj = + j and mj = —Each orientation of nuclear spin will interact, or couple, with the unpaired electron in such a way that the local magnetic field experienced by the electron is slightly different The magnitude of this difference is represented by a hyperfine coupling constant a, such that... 

The magnitudes of the hyperfine splitting parameters also yield information about the electron distribution in the molecule. The theory of the electron-nuclear coupling interaction was first worked out by Fermi, who showed that the constant a depended on the electron density at the nucleus. For a free hydrogen atom, a is given by the Fermi contact interaction in the forrn ... 

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