FT spectroscopy of wide lines

For wide line NMR, it is especially important to understand the fundamentals of FT spectroscopy because some of the aspects which can be ignored in high resolution FT spectroscopy are significant for wide lines. Even for the high resolution NMR spectroscopist, this section will provide additional understanding. 

Instrumentation is appropriately different for the wide line case. The demands on magnet resolution and stability are reduced but those on data acquisition and transmitter and receiver recovery are increased. While most high resolution FT systems use digitizers that can digitize at a maximum rate of 50 kHz or less, a MHz or greater rate may be required for the spectra of solids. 

In high resolution FT, the long duration of the FID and the fact that the spectrum usually consists of Lorentzian ab- 

Contrast the above situation with that of wide line FT NMR. First, we need the instrumental capabilities mentioned earlier. Secondly, often we are trying to obtain the shape of a single line or those of a small number of lines which may be complex. Therefore, we cannot presume to know the line shape in order to phase it properly. Similarly, an exponential time window function may alter the lineshape information. Third, the delay time used to avoid the pulse breakthrough in the FID is almost certain to be a significant fraction of the total acquisition time and must be taken into account. Let us deal with each of these difficulties in order. 

The phasing problem is usually overcome by a calibration of the required phase correction measured as a function of offset with a simple line from a liquid sample. This may not work for metallic samples which can have a signal with a phase different from non-metallic samples, not to mention the differences in the phase of the signal from different parts of 

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