Broad lines, measurement

The sinc fiinction describes the best possible case, with often a much stronger frequency dependence of power output delivered at the probe-head. (It should be noted here that other excitation schemes are possible such as adiabatic passage [9] and stochastic excitation [fO] but these are only infrequently applied.) The excitation/recording of the NMR signal is further complicated as the pulse is then fed into the probe circuit which itself has a frequency response. As a result, a broad line will not only experience non-unifonn irradiation but also the intensity detected per spin at different frequency offsets will depend on this probe response, which depends on the quality factor (0. The quality factor is a measure of the sharpness of the resonance of the probe circuit and one definition is the resonance frequency/haltwidth of the resonance response of the circuit (also = a L/R where L is the inductance and R is the probe resistance). Flence, the width of the frequency response decreases as Q increases so that, typically, for a 2 of 100, the haltwidth of the frequency response at 100 MFIz is about 1 MFIz. Flence, direct FT-piilse observation of broad spectral lines becomes impractical with pulse teclmiques for linewidths greater than 200 kFIz. For a great majority of... 

NMR Measurement of The Residual Water. The residual water obtained in Experiments No. 5 and No. 6 was measured with a broadline NMR spectrometer, in which, proton signal of the water gives a very broad line. The full width at half height of the NMR signal is 15750 Hz and 18000 Hz for samples obtained in Experiments No. 5 and No. 6, respectively. The line width for liquid water is normally less than 5 Hz while the line width for polycrystalline ice is 56000 Hz (39). Therefore, the residual water is expected to have a mobility closer to ice than to liquid water. The wider line given by sample obtained in Experiment No. 6 seems to agree with the expectation that the water is more immobile at higher electrolyte concentration. 

The 113Cd Ti values estimated for the various peaks varied from 10 to 50 ms and obeyed the qualitative dependence upon 1/R6 (R = Mn-Cd distance) of the dipolar relaxation mechanism expected to be operative. The broad line widths were also shown to have significant contributions from the T2 relaxation induced by Mn++, with both dipolar and contact terms contributing. The 113Cd shifts of the peaks assigned to different shells were measured as a function of temperature, and observed to follow a linear 1/T dependence characteristic of the Curie-Weiss law, with slopes proportional to the transferred hyperfine interaction constant A. 

The following data describe the pattern for dobutamine hydrochloride, where d is equal to the interplanar spacing measured in terms of Angstroms (A). The ratio I/It is the intensity of the X-ray maxima based upon a value of 100 for the strongest line. A b indicates a broad line resulting from failure to resolve two closely spaced diffraction maxima. 

In a very broad line, then, the size of the spin echo is proportional to the number of nuclear moments near go. If we change Hq, we change h by the same amount and thus sample nuclear moments at a different local field. By measuring the size of the spin echo as a function of Hq, we obtain the NMR lineshape, i.e., in this case, the distribution of the local field among the nuclear spins in the sample. 

The continuity of the linewidth over a large temperature range, above room temperature, that has previously been reported (IJ) and is further detailed here does not reveal any change in the vicinity of the a transition region (80-100°C). Major changes are found in broad line proton NMR experiments, which measure linewidths or second moments. ( ) There is, however, no discrepancy between these results since the a transition is a property of the crystalline regions. The proton measurements... 

Examination of the ESR spectra measured in this study, Figures 1 and 2, shows no indication of the dipolar broadened line at 77 K in the networks studied even when the samples were cooled to 77 K from ambient temperature during more than four hours. We particularly checked the S-band spectra for this line. We expect the dipolar broadening to be the same at the two frequencies but much more conspicuous at S-band because the spectrum from isolated ions is spread over a smaller range of magnetic fields at this microwave frequency. The absence of the broad line indicates that in all the networks measured Cu(ll) hydrated by freezable, or bulk, water is not detected. These results are in agreement with those presented in ref. 25 which indicate the absence of bulk water in water absorbed on silica gels with pores smaller than 6 nm. 

The broad line 2H NMR results, combined with the H and 29Si MAS-NMR results, confirm that acetone-d6 molecules are able to penetrate into the microporous channels of sepiolite, and cannot be removed by heating to only 60°C. This result is in agreement with a previous study that found, on the basis of BET surface area measurements, that molecules such water, ammonia, ethanol, benzene and pyridine were small enough to fit inside the microporous channels [10],... 

Measurements of 1H NMR of zinc and cadmium complexes, both in solution and of crystals, have been made. A broad-line 5H NMR study of [Zn(0H2)6][C104]2 over the 4.2-363 K temperature range confirms the basic octahedral symmetry of the cation, although some reorientation of the water molecules does occur.60... 

Fig. 14. Dependence of the relaxation times T2. and the fractions of protons with different mobility (f.) for unsaturated polyester on the curing time, as measured from broad line NMR ( ), Hahn spin-echo ( ) and Carr-Purcell pulse sequence (O)- Symbol x indicates the initial distribution of styrene and unsaturated polyester protons (adapted from Ref. S5))...

As pointed out in Chapter I, the NMR absorption spectrum for polymers in the solid state is generally very broad. In such cases the NMR is usually observed as the so-called broad-line spectrum. In this, the resonance is recorded by slowly sweeping the main static magnetic field H modulated with a small amplitude and frequency under a constant high-frequency subfield rotating perpendicularly to the main field. Figure 5 shows schematically the principle of the measurement for the broad-line NMR... 

The first derivative of a broad-line spectrum can be described in the three terms as a function of the strength of the main magnetic field in the measurement ... 

These findings are in broad agreement with the wide-line measurements by Genser (158) who from the second moment of the 27A1 line in hydrated zeolite Y calculated vQ = 390 kHz, but was not able to observe a signal in dehydrated zeolite. Gabuda et al. (137) observed increased values of vQ after dehydration of zeolites. For the hydrated and dehydrated analcime the values were 270 and 390 kHz, respectively for Na-X, 165 and 285 kHz and for Na-A, 75 and 165 kHz. 

As can be seen, for both samples the crystalline mass fraction (orthorhombic plus monoclinic) agrees well with that estimated from the density measurements and broad-line H NMR analysis. The thicknesses of the interphases are 3.8 and... 

Spectrum averaging is probably the most effective way to increase S/N (Fig. 15.7), and is particularly important when measuring spectrum with broad lines. 

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