Lineshape inhomogeneous

Figure 34 shows spectra of TA and SOL from a 24-year-old male volunteer recorded at 1.5 T (a) and 3.0 T (b). Besides the clearly improved SNR, which is elevated by a factor of 1.7 to 1.8 at 3.0 T, distinct differences can be observed for the two magnetic field strengths In both muscles, IMCL and EMCL are clearly better separated at 3.0 T as the methylene resonance of IMCL shows smaller natural linewidths (in ppm). However, EMCL signals remain with a broad lineshape in TA as well as in SOL, since the lineshape is dominated by susceptibility induced static field inhomogeneities. Crs and TMA signals are... 

Spectra recorded from smaller VOI (down to 0.25 ml) with careful positioning in regions without fatty septa provide a clearly decreasing EMCL signal contamination, resulting in improved visibility of IMCL in SOL at 3.0 T (see Fig. 36). Separate depiction of IMCL improves quantification of this lipid compartment, as inaccuracies due to the inhomogenous lineshape and resulting contaminations of EMCL can be avoided. 

Suppose that a pulse Fourier transform proton NMR experiment is carried out on a sample containing acetone and ethanol. If the instrument is correctly operated and the Bq field perfectly uniform, then the result will he a spectrum in which each of the lines has a Lorentzian shape, with a width given hy the natural limit 1/(7tT2). Unfortunately such a result is an unattainable ideal the most that any experimenter can hope for is to shim the field sufficiently well that the sample experiences only a narrow distribution of Bq fields. The effect of the Bq inhomogeneity is to superimpose an instrumental lineshape on the natural lineshapes of the different resonances the true spectrum is convoluted by the instrumental lineshape. 

Multiple-pulse measurements were performed on both the LP and HP samples at 20° and — 80° C, and when no differences were noted, lower temperature measurements were performed only on the LP sample. Multiple-pulse spectra for the LP sample are illustrated in Figure 4 together with the eight-pulse spectrum of the reference used for the low-temperature measurements, Ca(OH)2. The lineshapes observed are quite broad, and the line center is a function of temperature. The line width was separated into three contributions by performing three related multiple-pulse measurements (I). These indicated that the main contributions to the linewidth came from both relaxation and second-order dipolar effects. The maximum possible field inhomogeneity Hamiltonian is estimated to be less than 16 ppm by this means, which indicates that the com-... 

Low frequency spectra of liquids are notably deficient of any structure, and it has long been hoped that a technique would be discovered that provides the same type of line narrowing enjoyed in echo-based electronic and NMR spectroscopy. Tanimura and Mukamel observed that such a technique was possible, and proposed a two-time interval, fifth-order Raman pulse sequence capable of distinguishing, for example, inhomogeneous and homogeneous contributions to the lineshape.[4] The pulse sequence, shown in Fig. 1, is simply an extension of conventional time-domain third-order Raman-based methods. At the... 

Deuterated PB networks filled with carbon black have been investigated recently [74]. The 2H NMR lineshape is different from that in unfilled elastomers an asymmetric doublet is observed as the sample is uniaxially stretched (A,=1.8)). This asymmetry is related to the presence of carbon black fillers, which induce magnetic inhomogeneities. 

The application of the reference deconvolution technique to overcome the effect of magnetic field inhomogeneity in high-resolution NMR has recently been reviewed by Metz et al.21 In this technique, the observed resonance lineshape from a single resonance line is used to deconvolve the observed lineshapes to produce the Lorentzian lineshapes associated with liquid samples. 

A distinction arises in the description of the lineshape when the dense, optically inactive manifold is replaced by a sparse one, corresponding to the intermediate case 15>. This may apply to small molecules such as SO2 and NO2, and also to large molecules characterized by a small energy gap between the two interacting electronic states, such as naphthalene 16> V) and 3,4-benzpyrene 18>. According to Jortner, Rice and Hochstrasser 8>, separate, inhomogenously broadened lines are predicted for the intermediate case. 

An inhomogeneous broadening refers to the collective motion frequency of the adsorbate and is the consequence of an inhomogeneous distribution of individual molecules either due to heterogeneity of adsorption sites or to nonhomogeneous in-termolecular distances. Whilst for a perfect ordered layer a sharp, symmetric band is expected, random occupation, island formation, and repulsive or attractive interactions give rise to a variety of characteristic lineshapes [21]. 

In order to resolve beyond mean-field processes in BEC, we must overcome inhomogeneous broadening, which masks homogeneous lineshapes we want to measure. One possibility is to resolve the radial modes (Sec. 1), or for appropriate parameters, the use of our echo spectroscopy scheme (Sec. 6). 

---