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Dynamic-angle spinning

02 = 63.43° (k = 5) is special because it allows efficient CP for signal enhancement prior to the DAS sequence. There are several ways in which the DAS spectra can be acquired one can acquire the entire echo, which means that the resulting 2D spectmm will be sheared. Some additional processing is then required to obtain an isotropic spectrum in FI. The advantage of acquiring the entire echo is that the second-order information is retained. Hence the 2D data set has improved the resolution whilst providing second-order quadrupolar information as well. Alternatively, the acquisition could also start at [Pg.92]

At this point an echo forms but the coefficients of the isotropic terms are different and so are not refocused at this point. This has important consequences for the experiment. The isotropic part of the quadrupole frequency is [Pg.94]

Under MAS the terms involving P2(cos0) (for both the quadrupole and chemical shift) and P4(cos0) are refocused along the ridge but there are isotropic terms. The isotropic parts of both the chemical shift Aviso and the isotropic second-order quadrupole effects v, are scaled. These scale factors (SF) are for the chemical shift [Pg.95]

Numerical calculations have been carried out on the effect of the angle on the conversion efficiency. The work of Amoureux and Fernandez (1998) is summarised in Table 2.9. One of the key observations is that the efficiency of the flip angles shows no real dependence on r. However, the conversion is quite an inefficient process so that the overall sensitivity of the experiment is poor relative to one-pulse experiments and much effort has gone into improving the excitation and reconversion efficiency. As I increases, the optimum flip angle for maximum excitation decreases. [Pg.96]

Since both excitation and conversion are dependent on r, MQ spectra are normally not directly quantitative, so great care has to be taken to interpret the spectra. The situation will generally improve as the applied rf field increases. Since the 2D data set contains the anisotropic information, lineshapes can be analysed and the quadrupolar parameters deduced. The lineshape will show distortion as there will be crystallites whose orientation is such that their quadrupolar frequency is zero and will not contribute. Apart from the excitation and the conversion, the actual coherence pathway [Pg.96]


Mueller, K.T., Wooten, E.W., and Pines, A. (1991) Pure-absorption-phase dynamic-angle spinning. /. Magn. [Pg.168]

In order to remove the anisotropic effects of quadrupolar interactions which can obscure MAS spectra other techniques such as Double Rotation (DOR) [18, 19], Dynamic Angle Spinning (DAS) [18] or Multiple Quantum Magic Angle Spinning (MQMAS) have to be employed. Of these the most simple to apply practically is MQMAS, which can be conducted on a standard MAS-equipped NMR spectrometer. A number of texts and review papers discuss MQMAS in significant technical detail [20, 21]. [Pg.201]

In Dynamic Angle Spinning (DAS) [53-55], the sample is rotated sequentially about two different axes, ffi and ff2, which are chosen so that... [Pg.12]

In this review, we shall introduce some basic concepts about sohd-state NMR of half-integer quadrupolar nuclei and discuss the most useful and promising methods presently available to study them. These include older methods, such as Double Rotation (DOR) and Dynamic Angle Spinning (DAS), and novel techniques including MQMAS, Quadrupolar Phase Adjusted Spinning Sidebands QPASS, SateUite Transition (ST) MAS and Inverse-STMAS NMR, and Fast Amplitude Modulation (FAM). We also discuss several techniques based on dipolar interactions between quadrupolar and spin-1/2 nuclei, such as Cross-Polarization (CP) MQMAS, MQ Heteronuclear Correlation Spectroscopy... [Pg.142]

Grandinetti PJ, Baltisberger JH, Faman 1, Stebbins JF, Werner U, Pines A (1995) Solid-state O magic-angle and dynamic-angle spinning NMR study of the Si02 polymorph coesite. J Phys Chem... [Pg.238]


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