Line-broadening, causes

The line broadening caused by partial motional narrowing can be distinguished from that due to isotropic reorientation at a reduced rate by appropriate magic angle spinning experiments. 

It is obvious that the best resolution is obtained from samples that contain no insoluble impurities, and no paramagnetic materials. The line broadening caused by soluble paramagnetic impurities11 may be... 

NMR analysis of a paramagnetic biomolecule may require modifications to the standard experiments. In some cases, this is to compensate for deleterious line broadening caused by unpaired electrons, which interferes with detection of resonances and NOEs. In other cases, modifications are made to take advantage of the effects of unpaired electrons to selectively observe nuclei in the vicinity of the paramagnetic metal. The effects of the metal on the NMR spectrum depend largely on the Xs value, which determines amount of linebroadening (equations 16 and 17). For systems with relatively short tg, few, if any, modifications need to be made, whereas study of systems with long tg require specially tailored experiments to obtain any information on nuclei in the vicinity of the metal site. ... 

The results of the present work are summarized in Table L The observed experimental Unewidths, when corrected lor line broadening caused by finite absorber thickness, compare quite well with twice the natural width of the Mossbauer gamma rays,... 

Infrared spectrosoipy performed at 0.3 cm resolution on 90% samples displayed an increased line width for all the four main features but no essential change in the line shapes. Table 1 lists the observed widths. For a light carbon molecule one would expect line broadening caused by the various possible isotopic modifications (isotopomers) of the molecule. Instead we noted that the increase in line-width (e.g. for the 528 cm" feature) is rather lim-... 

We can see easily from this argument that if there is a range of linewidths in the spectrum we cannot find a value of the linebroadening which is the optimum for all the peaks. Also, the extra line broadening caused by the matched filter may not be acceptable on the grounds of the decrease in resolution it causes. Under these circumstances we may choose to use sufficient line broadening to cut off the excess noise in the tail of the FID, but still less than the matched filter. 

EPR spectra of chlorophyll and tyrosine radicals are shown in Figs. 1 and 2. In these examples, the radicals are immobilized in the EPR time scale owing to the large size of the protein. Although the EPR spectra shown in Figs. 1 and 2 were measured on frozen samples, the EPR spectra are unchanged if the measurements are made on liquid samples, except for some line broadening caused by faster spin relaxation rates. 

We filter a heterogeneous solution before putting it in our NMR tube. Adding a tiny splash of extra solvent to a saturated solution to get below the precipitation threshold may also help minimize the line broadening caused by the microscopic nucleation of colloidal or crystalline particles present in saturated solutions. Alternatively, we... 

The line broadening caused by interactions is largely eliminated... 

Evaluation of NMR measurements on Al is facilitated by the fact that the spectrum is comparatively simple the line broadening caused by quadrupole relaxation is extremely small even in solvent mixtures. This permitted the use of this method to distinguish between the different solvates formed in solvent mixtures. The coordination number of the aluminium ion is known to be 6 in both dimethylformamide and dimethyl sulphoxide solution [Mo 67, Mo 68, Th 66c]. In a mixture of these two solvents, however, the solvating effect of DMSO is more marked than that of DMF [Gu 74]. The solvation conditions are also influenced by dilution with an inert solvent. Thus, for instance, if a solution containing DMSO and DMF as solvents is diluted with nitromethane, which can be regarded as inert from the aspect of solvation, then the earlier difference between the solvating powers of the two donor solvents no longer appears. This experiment also reflects the effect of the solvent-solvent interaction on the solvation of a solute. 

Table 7 gives the chemical shifts, the paramagnetic H NMR shifts and the line width of some lanthanide tricyclopentadienyls. The extreme line broadening caused by very long relaxation times of Gd and Er are the reason, that no resonances are detected for the gadolinium and the erbium derivatives (Von Ammon et al., 1969 R.D. Fischer, 1973). 

Fig. 3.20. Line broadening caused by the curvature of wave fronts...

Combined laser-microwave spectroscopy based on optical pumping was also performed in the solid state. Spectral line broadening caused, e.g., by strain and phonon interaction, can be overcome by extreme cooling and specific site selective procedures. Very narrow lines are attainable particularly in the spectra of rare earth ions doped to crystals in low concentration. Rare earth ions, therefore, play an important role in solid state spectroscopy, as will be illustrated in the course of this section. 

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