Broad Lines

In the linear approximation there is a direct Fourier relationship between the FID and the spectrum and, in the great majority of experunents, the spectrum is produced by Fourier transfonnation of the FID. It is a tacit assumption that everything behaves in a linear fashion with, for example, imifonn excitation (or effective RF field) across the spectrum. For many cases this situation is closely approximated but distortions may occur for some of the broad lines that may be encountered in solids. The power spectrum P(v) of a pulse applied at Vq is given by a smc fiinction 18]... 

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... 

A monochromator is useful not only for removing unwanted lines from the X-ray source but also for narrowing the otherwise broad lines. For example, each of the MgXa and AlXa doublets is unresolved and about 1 cY wide at half-intensity. A monochromator can reduce this to about 0.2 cY This reduction of the line width is very important because in an XPS specttum, unlike an ultraviolet photoelectron specttum, the resolution is limited by the line width of the ionizing radiation. Unfortunately, even after line narrowing to 0.2 cY... 

There are hundreds of primary battery manufacturers, most of which are limited to a specialty product or a limited national market. However, a number of multinational battery suppHers have manufacturing faciUties in many countries and a broad line of products. Table 4 Hsts the companies having sales of primary batteries of greater than 100 million per annum together with the regions of their headquarters and their product lines. 

In the case that SWCNTs were produced by laser ablation with Co and Ni, a very weak and narrow signal was superposed on the main broad line. To confirm that this narrow line is associated with SWCNTs, the sample was vacuum-annealed at 1500°C to remove the remaining Co and Ni. 

Variable temperature NMR studies of [IrCl2(PMe2Ph)4]+ (XXV L = PMe2Ph) show a broad line in the 31P spectrum at room temperature but on cooling to 80°C a mass of sharp lines are observed, owing to three to four rotational isomers (Figure 2.89) the predominant ABCD pattern is... 

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

Benzene-ring orientation 100 Boundary layer 151 Broad line NMR 197 Buckling of fibrils 140... 

In another study (Ji8), it was found that graphite does not intercalate with neat XeF2 or with solutions of XeFa in acetonitrile. However, reaction with solutions of XeF2 in AHF led to copious xenon evolution, indicating that oxidation does take place, even at room temperature. Broad-line, F- and H-NMR spectra (Ell) showed the presence of both XeF2 and HF in the product, but no definite stoichiometry could be as-... 

Compounds 225a-f showed interesting dynamic phenomena on the NMR time scale with broad lines at room temperature and appearance of two sets of sharp peaks at -50 °C corresponding to conformers 226 and 227 (Fig. 3). By contrast, 225 g-1 exist essentially as one conformer. These results show that the presence of a Me substituent adjacent to the 0 atom in ring B and syn to the ring junction hydrogen (see 225 g) prejudices the molecule in favor of conformer 226, thus placing the Me substituent pseudoequatorially (cf. 226, = Me). Sim-... 

The process of exponential multiplication just described produces a rapid decay of the FID and the production of broad lines suppressing the decay of the FID gives narrow lines and better resolution, with increased noise level. An alternative approach to resolution enhancement is to reduce the intensity of the earlier part of the FID. Ideally, we should use a function that reduces the early part of the FID, to give sharper lines, as well as reduces the tail of the FID, to give a better signal-to-noise ratio. 

The situation becomes less complicated in case of Rh deposition at 90 K. For low coverage only one peak at 1994 cm is observed while at high coverage (see Fig. 3a) a broad band centered aroimd 2075 cm and a sharp, prominent peak at 2117 cm also observed at 60 K, is found [15]. fii addition, the spectriun shows a sharp band of lower intensity at 2097 cm Since all bands are located above 1950 cm the CO molecules are predominantly bound terminally in all cases. The broad line, which changes somewhat in shape upon annealing to 300 K (see Fig. 3a), is due to CO on larger Rh particles [33,34] in line with observations on technical catalysts [35-40]. 

We have shown in the preceding section that the IR spectra of well-defined metal carbonyls provide valuable information of the environment of the deposited metal atom. However, IR signals of CO molecules adsorbed on larger particles suffer from broad lines, which hamper a more detailed analysis of the data. In the forthcoming section we will present results on cobalt particles where carbonyl species are formed on larger particles containing hundreds of atoms. 

Zeolites. In heterogeneous catalysis porosity is nearly always of essential importance. In most cases porous materials are synthesized using the above de.scribed sol-gel techniques resulting in so-called amorphous catalysts. Porosity is introduced in the agglomeration process in which the sol is transformed into a gel. From X-ray Diffraction patterns it is clear that the material shows only weak broad lines, characteristic of non-crystalline materials. Silica and alumina are typical examples. Zeolites are an exception they are crystalline materials but nevertheless exhibit high (micro) porosity. Zeolites belong to the class of molecular sieves, which are porous solids with pores of molecular dimensions, i.e., typically the pore diameter ranges from 0.3 to 10 nm. Examples of molecular sieves are carbons, oxides and zeolites. 

For arylpolysilanes the results are quite different.(34) The 29Si NMR for (PhSiMe)n is shown in Figure 6 it consists of three broad lines with relative intensity 3 3 4, each line evidently containing a cluster of resonances. The patterns for other aryl-alkylpolysilanes differ, but in general two or three broad resonances are found none of the aryl compounds studied so far has given a symmetrical pattern like those observed for the alkylpolysilanes of Figure 5. 

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. 

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