Satellite-transitions

NMR studies carried out on nuclei such as FI, and Si this does not really impose any limitation on their observation. Broader spectral lines can be reproduced by pulse teclmiques, provided that corrections are made for the RF-irradiation and probe responses but this requires carefiil calibration. Such corrections have been most extensively used for examining satellite transition spectra from quadnipolar nuclei [11]. 

Physical background. MAS will narrow the inliomogeneously broadened satellite transitions to give a series of sharp sidebands whose intensity envelopes closely follow the static powder pattern so that the quadnipole interaction can be deduced. The work of Samoson [25] gave real impetus to satellite transition spectroscopy by showing that both the second-order quadnipolar linewidths and isotropic shifts are fiinctions of / and Some combinations of / and produce smaller second-order quadnipolar effects on the satellite lines than... 

Advantages. The experiment can be carried out with a conventional fast-spuming MAS probe so that it is straightforward to implement. For recording the satellite transition lineshapes it offers better signal-to-noise and is less susceptible to deadtime effects than static measurements. As the effects differ for each value, a single satellite transition experiment is effectively the same as carrying out multiple field experiments on the central transition. 

Figure Bl.12.13. MAS NMR spectra from kyanite (a) at 17.55 T along with the complete simulation and the individual components, (b) simulation of centreband lineshapes of kyanite as a fiinction of applied magnetic field, and tire satellite transitions showing (c) the complete spiimmg sideband manifold and (d) an expansion of individual sidebands and their simulation.

Satellite transition MAS NMR provides an alternative method for detennining the interactions. The intensity envelope of the spimiing sidebands are dominated by site A2 (using the crystal structure nomenclature) which has the smallest Cq, resulting in the intensity for the transitions of this site being spread over the smallest... 

Figure 5.4 Part of the microwave spectmm of cyanodiacetylene. (The many satellite transitions in each group are due to the molecule being in not only the zero-point vibrational state but also a multitude of excited vibrational states.) (Reproduced, with permission, from Alexander, A. J., Kroto, H. W. and Walton, D. R. M., J. Mol. Spectrosc., 62, 175, 1967)...

There are two further effects on K emission XRF which become more important with decreasing nuclear charge. One is the appearance of weak satellite transitions, to lower wavelengths of the main transitions, occurring in the small proportion of doubly ionized atoms which may be produced by the initial X-ray bombardment. The other is a tendency for some transitions to be broadened into bands, rather than the usual sharp lines, due to the... 

Satellite transition magic angle spinning (STMAS) Selection of coherences... 

In 2006 Wimperis et al. proposed a method called satellite transitions acquired in real time by MAS (STARTMAS) [142, 202], which allows for the real-time acquisition of high-resolution NMR spectra of spin-3/2 nuclei under MAS. This method combines a train of pulses, similar to CPMG [109, 110], with sample rotation at the magic angle to refocus the quadrupolar broadening in a series of echoes, while allowing the isotropic quadrupolar shift and chemical shift to evolve. 

Gan, Z. (2000) Isotropic NMR spectra of half-integer quadrupolar nuclei using satellite transitions and magjc-angle spinning. /. Am. Chem. Soc., 122, 3242-3243. 

Gan, Z. (2001) Satellite transition magic-angle spinning nuclear magnetic resonance spectroscopy of half-integer... 

In many cases the temperature dependence of the quadrupolar coupling constant is an indicator of dynamic processes, because the symmetry around the lithium cation is affected by motions which are fast on the NMR time scale. If the rate of these processes exceeds 1/x, the effective symmetry around the lithium cation increases and a decrease in x( Li) results. In Li MAS spectra, a broadening of the satellite transitions can be observed which eventually disappear completely if the rate of the dynamic process comes in the order of the quadrupole frequency. This behaviour was observed for the THF solvated dimer of bis(trimethylsilylamido)lithium, where the Li MAS spectrum at 353 K shows only the central transition and the sidebands caused by CSA and homonuclear Li- Li dipole coupling (Figure 27) . The simulation of the high-temperature spectrum yielded —20 ppm and 1300 Hz for these quantities, respectively. The dipole coupling agrees closely with the theoretical value of 1319 Hz calculated from the Li-Li distance of 2.4 A, which was determined by an X-ray study. 

Figure 4 Schematic representation of the populations of the nuclear spin energy levels of a quadrupolar nucleus with spin 5/2 (such as Mg) under a strong magnetic field and a perturbative quadrupole coupling showing (A) populations at thermal equilibrium, (B) populations after complete saturation of the satellite transitions, and (C) populations after complete inversion of the satellite transitions, following the order first, inversion of STl and ST4 and then inversion of ST2 and ST3. The numbers at left of each level (named pj in the text) are proportional to the population of that level, with —hVl/ 2k T= 0. ...

S. E. Ashbrook and S. Wimperis, Fligh-resolution NMR of quadrupolar nuclei in solids the satellite-transition magic angle spinning (STMAS) experiment. Prog. Nucl. Magn. Reson. Spectrosc., 2004, 45,53-108. 

Selective population or polarization transfer (abbreviation SPT) was first achieved for chloroform [51] by brief irradiation of one of both 13C satellites in the proton NMR spectrum before recording the 13C—1H doublet as FID signal. In this experiment, the decoupling pulse inverts the population of the proton precession states connected by the irradiated satellite transition (Fig. 2.43(b, c)). The two SPT experiments shown for the 13C —H doublet of chloroform in Fig. 2.43 (b, c) give an impression of the signal enhancement achievable by population transfer in comparison to a normal 13C NMR spectrum... 

Half-integer quadrupolar nuclei NMR central transition, 1, 457, 1, 464 NMR satellite transitions, 1, 455 Half-sandwich complexes... 

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