Lineshape simulation

In Fig. 4 we compare the adiabatic (dotted line) and the stabilized standard spectral densities (continuous line) for three values of the anharmonic coupling parameter and for the same damping parameter. Comparison shows that for a0 1, the adiabatic lineshapes are almost the same as those obtained by the exact approach. For aG = 1.5, this lineshape escapes from the exact one. That shows that for ac > 1, the adiabatic corrections becomes sensitive. However, it may be observed by inspection of the bottom spectra of Fig. 4, that if one takes for the adiabatic approach co0o = 165cm 1 and aG = 1.4, the adiabatic lineshape simulates sensitively the standard one obtained with go,, = 150 cm-1 and ac = 1.5. 

Due to the tetrahedral arrangement of the windows within the cage, tetrahedral jumps of the cations are feasible. This jump model is confirmed by the averaged parameters obtained by lineshape simulations of the broad lines at 295 and 813 K. Cq is reduced at 813 K to about half of its original value at 295 K, and the averaged asymmetry parameter, (77), is 1. Especially (77) is a very sensitive parameter on jump angle due to the steepness of the curve in Fig. 8a. 

The case of intermediate motional rates has not yet been addressed, but should be a fairly simple extension, merely requiring details of the lineshape simulation to be derived for this case. 

For this reason, the study in question19 examined a sample of high-density polyethylene that was iso topically labelled with, 3C so as to produce isolated 13C spin pairs. Static 13C powder lineshapes were then observed as a function of temperature. Analysis of these by lineshape simulation shows that, indeed, the polyethylene chains do undergo 180° chain flips. The static lineshapes in this case result from the sum of chemical shift anisotropy and dipolar coupling. However, the chemical shift anisotropy is known and, as mentioned previously,... 

For these complexes, the isotropic and 15N chemical shifts and the 15N chemical shift tensor elements were measured as a function of the hydrogen bond geometry. Lineshape simulations of the static powder 15N NMR spectra revealed the dipolar 2H-15N couplings and hence the corresponding distances. The results revealed several correlations between hydrogen bond geometry and NMR parameters which were analysed in terms of the valence bond order model. It was shown that the isotropic 15N chemical shifts of collidine and other pyridines depend in a characteristic way on the N-H distance. A correlation of the and 15N... 

After the 2D spectra have been obtained and the axes labelled by a method of choice, the centre of gravity along Fi and F2 can be used to derive the chemical shift and second-order quadrupolar effect, according to Eqs. (57) and (58) or specifically by Eqs. (59) or (60). However, more information can be obtained by summing slices parallel to F2 of specific 2D peaks. These result in quadrupolar MAS lineshapes for each site separately. From the second-order quadrupolar MAS lineshapes, x fd 17 can be unambiguously determined. Lineshape simulations can be performed, for example,... 

Among two-dimensional experiments, wideline exchange spectroscopy plays a prominent role in H NMR [1, 4, 61-64]. By correlating the frequency distributions at two different times, any changes in the resonance frequency due to reorientation can be detected in the off-diagonal intensity pattern. With the aid of lineshape simulation and by comparing different mixing times, detailed conclusions about the type and rate of motion can be drawn, as illustrated in Section 6.2.5 and Fig. 6.2.2. 

The effect of alkali promoters on dynamics of chemisorbed hydrogen was determined in terms of an exchange parameter which was determined from lineshape simulations as described in [4]. The exchange parameters determined for 0 and 66 at. % K promoted catalysts at a hydrogen coverage of 0.8 were listed in Table 1. 

In contrast to the SNMR method, it is crucial to measure an undistorted polycrystaUine static spectrum in order to have a reUable spectral analysis when the effects of finite RF pulses and detection bandwidth are ignored in the numerical simulation. Since Co static powder spectra in general have well-defined singularities and therefore are suitable for lineshape simulation, the issue of spectral distortion seems to be particularly important for Co NMR practitioners. In this section we will give a brief account of lineshape analysis, including experimental considerations and precautions for numerical simulations. 

Numerical simulation. Lineshape simulations are useful for spectra with well-defined singularities. Initial parameters for lineshape simulations may be obtained from the published NMR data of similar systems. Alternatively, moment analysis of the spectra could produce a useful initial guess. Since the degree of freedom involved in the spectral analysis of a Co spectrum is large,... 

J. Hirschinger, D. Enghsh, Differentiation of models of rapid molecular motion by 2H NMR lineshape simulations, J. Magn. Reson. 85 (1989) 542—553. 

We are using NMR spectroscopy in conjunction with lineshape simulations to investigate the structure and dynamics of organometallic compounds incorporated into a variety of host lattices. Here, the potential of this approach is illustrated with results from studies of perdeuterated Fecp2 and Cocp2 different crystalline environments. 

This can be done by carrying out lineshape simulations. However, in general this is not done because a Zeeman magnetization exchange experiment is more... 

In many cases, not all these parameters are known for the specific spin system under investigation. Therefore, two techniques that may be employed when a lineshape simulation is desirable are (i) a simulation based on known chemical shielding tensors (a), /-coupling constants, and values, where... 

In spite of the results of the preceding example, the lineshape simulation method has rarely been used in practice, mainly because the R d values are too small to result in splittings. In such cases, the exchange curve method discussed below is the standard technique for extracting the dipolar coupling constant under RR conditions. 

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