Knight shift experimental values

From a very general outlook, one can argue that the NMR studies of quadrupolar nuclei present in nanoscale semiconductors should offer a more incisive look into the chemical and electronic structure than do studies of spin-1/2 nuclei. The rationale is that quadrupolar nuclei can report on the same chemical, hyperftne, or Knight shifts and dipolar or indirect couplings as observed for spin-1/2 nuclei, but also provide an additional dimension of information in terms of the NQCC and associated EFGs. Although not yet reported, DFT calculations of both chemical shifts and NQCC values for the same nuclei in nano-semiconductors should provide a more stringent comparison of theoretical and experimental results, particularly if the two parameters can be correlated experimentally, as seems feasible. 

The absolute chemical shifts of protons in diamagnetic solids are typically near 30 ppm (28), and the Knight shift caused by conduction electrons through contact interaction is estimated to be —31.2 ppm, using the experimental T1T value of 180 JK-sec and the Korringa relation (29) ... 

Table 15. Ratio of the s partial charge densities q / Ep) to the total partial densities qy(Ep) for electronic states at the Fermi level Ep and Knight shifts K, (in %) for intermetallic Zintl compounds AB The calculated direct contribution K - and the total spin contribution K< are listed. For comparison the Knight shift found experimentally in the Zintl (K ) phases and in the pure metals (KJ" ) are given too. For the AB compounds the theoretical values are shown for both the defect (de) and the stoichiometric (st) phases...

Pronounced crystal-field effects were observed in the paramagnetic phase NMR for intermetallic compounds of Ce, Pr, Sm or Tm. Crystal-field effects for Tm in TmAlj have been analysed by de Wijn et al. (1970) by a combination of the temperature dependences of the Al Knight shift and of the magnetic susceptibility. These authors also analysed the quadrupole interaction for the Al site in the cubic CujAu structure. Comparing the experimental value e qQ/h = 7.6 MHz with the point-charge model value (Abragam 1961)... 

In Table 2 we show some results on the effect of polymerization on the Si shift, taken from Moravetski et al. (1996). These were obtained using the GIAO method with polarized triple zeta basis sets at polarized double zeta Hartree-Fock geometries. The experimental values are taken from Harris and Knight (1983). 

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