Dispersion mode

Hanna, S. R. and D. Strimaitis, 1989, Workbook of Test Cases for Vapour Cloud Dispersion Modes, CCPS, New York. 

The deuterium line of the deuterated solvent is used for this purpose, and, as stated earlier, the intensity of this lock signal is also employed to monitor the shimming process. The deuterium lock prevents any change in the static field or radiofrequency by maintaining a constant ratio between the two. This is achieved via a lock feedback loop (Fig. 1.10), which keeps a constant frequency of the deuterium signal. The deuterium line has a dispersion-mode shape i.e., its amplitude is zero at resonance (at its center), but it is positive and negative on either side (Fig. 1.11). If the receiver reference phase is adjusted correcdy, then the signal will be exactly on resonance. If, however, the field drifts in either direction, the detector will... 

Figure 1.10 (a) The dispersion mode line should have zero amplitude at resonance, (b) The deuterium lock keeps a constant ratio between the static magnetic field and the radiofrequency. This is achieved by a lock feedback loop, which keeps the frequency of the deuterium signal of the solvent unchanged throughout the experiment. 

Figure 1.11 The dispersion-mode line shape showing the zero amplitude at the center of the peak but nonzero amplitude on each side.

Figure 3.10 Effect of different window functions (apodization functions) on the appearance of COSY plot (magnitude mode), (a) Sine-bell squared and (b) sine-bell. The spectrum is a portion of an unsymmetrized matrix of a H-COSY I.R experiment (400 MHz in CDCl, at 303 K) of vasicinone. (c) Shifted sine-bell squared with r/4. (d) Shifted sine-bell squared with w/8. (a) and (b) are virtually identical in the case of delayed COSY, whereas sine-bell squared multiplication gives noticeably better suppression of the stronger dispersion-mode components observed when no delay is used. A difference in the effective resolution in the two axes is apparent, with Fi having better resolution than F. The spectrum in (c) has a significant amount of dispersion-mode line shape.

Dispersion mode A Lorentzian line shape that arises from a phase-sensitive detector (which is 90 out of phase with one that gives a pure-absorption-mode line). Dispersion-mode signals are dipolar in shape and produce long tails. They are not readily integrable, and we need to avoid them in a 2D spectrum. 

Lorentzian line shape The normal line shape of an NMR peak that can be displayed either in absorption or dispersion mode. 

CXRS can also be employed in an angular dispersive mode (or both angular dispersive and energy dispersive). In this mode, a single-energy photon source. 

There are two components of the transverse nuclear magnetization one in phase with the field H, and one ir/2 out of phase with Hi. The former is known as the dispersion mode or u mode magnetization, and the latter as the absorption mode or v mode magnetization. That is, referring to Fig. 2, will lag or lead Hi as the resonance is traversed. The magnetic radiofrequency susceptibilities are defined by... 

Figure 6 illustrates a block diagram of a crossed-coil variable frequency spectrometer and associated electromagnet. A calibrator circuit 66) is useful for intensity calibration of absorption and dispersion mode signals. A calibrator circuit for the Pound-Knight type of spectrometer is also used... 

The Pound-Knight type of spectrometer has the disadvantage that the dispersion mode is not observed. The dispersion mode is important for the study of solids, since it does not saturate as readily as the resonance absorption in most solids 46), and in some cases (long thermal relaxation time) is the only mode that gives a measurable signal. On the other hand, high temperatures (up to 600°) are more conveniently attained with the Pound-Knight type spectrometer the conventional crossed-coil versions have been somewhat limited (up to 300°) in this respect. 

Fig. 11. A powder pattern of Al NMR in a- AI2O1 at NMR frequency of 7.20 me./ second (/fg = 6490 gauss) the magnetic field increases from left to right with a total scan of about 1500 gauss. This is the dispersion mode audio signal at Hi = 0.5 gauss and is the absorption envelope except at certain points as described in Section II,C,2 109).

The behavior of the dispersion mode derivative is also consistent with a proton dilute spin system, since if only a small fraction of the possible lattice sites are randomly occupied the majority of the protons will experi-... 

It may be useful to make some explanations on data processing to prepare good D-HMBC spectral data. Sine-bell window is usually employed for processing of HMBC data to give power-mode spectra as shown in fig. 6(a), because they consist of absorption-mode cosine) and dispersion mode sine) signals for both the t and t2 axes. This procedure causes a considerable loss of signal to noise ratio when cross peaks appear as broad ones and when digital resolution is poor as used for ordinary HMBC measurement. 

Figure 1 Schematic representation of polymeric and AMP dispersant mode of action...

Tullis (Ref 26) investigated both of these approaches to a single event FAE and proposed a concept best described as a one-step automatic two-event FAE. Here the second-event explosive is replaced by a very highly hypergolic oxidizer under the implosive dispersal mode. The technique is a one-step process since only one explosive charge need be detonated. The mechanism, however, proceeds via two events as the explosive charge causes a dual dispersal ... 

Intensity measurements using rapid-passage dispersion mode spectra have been little explored to date. It became necessary, therefore, to study the quantitative aspects of C13 NMR. Our early work was limited to measurements on alkyl aromatic and hydroaromatic compounds. The results of intensity measurements on the C13 spectra of 15 compounds are illustrated graphically in Figure 2. Each point is the average of measurements on at least eight spectra, four of which were obtained with sweep increasing and four... 

The solution of eq. (2.11) is a complex function. FFT computation therefore yields both real and imaginary PFT NMR spectra, v(co) and i u(to), which are related to the absorption and dispersion modes of CW spectra. The two parts of the complex spectrum are usually stored in different blocks of the memory and can be displayed on an oscilloscope to aid in further data manipulations. 

The real and imaginary spectra obtained by Fourier transformation of FID signals are usually mixtures of the absorption and dispersion modes as shown in Fig. 2.13 (a). These phase errors mainly arise from frequency-independent maladjustments of the phase sensitive detector and from frequency-dependent factors such as the finite length of rf pulses, delays in the start of data acquisition, and phase shifts induced by filtering frequencies outside the spectral width A. 

Fig. 2.13 (b, c) illustrates a phase correction. For correcting the phase, either the real or the imaginary part of the spectrum can be used. Correction of the real part for the absorption mode yields the dispersion mode in the imaginary part and vice versa (Fig. 2.13). 

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