FID Manipulation FT, EM, SINE BELL CH2 Signal of

The signal (FID, free induction decay) resulting from an NMR experiment contains the original data which are stored in the computer, and after the Fourier transformation (FT) we obtain the NMR spectrum itself. 

We can manipulate the FID mathematically in various ways before Fourier transformation, in order to optimize the spectrum with respect to the line-width or the lineshape. 

EM affects the linewidth and is often also known as a line broadening function LB. A positive value of LB (here 0.8 and 1.9 Hz) broadens the lines, a negative value (here -0.3 Hz) sharpens them however, never forget that we are only modifying the information present, so that a decrease in the line-width is automatically accompanied by an increase in the baseline noise. This becomes clear immediately when we see the spectra of the OCH2 multiplet shown in Fig. 6. 

Fourier transformation without data manipulation leads to the multiplet at the bottom (a), which shows more fine structure when a negative LB value is used (b). The spectrum in the middle (c) results from use of the SSB function, and now all eight lines are clearly visible as the linewidth is much smaller. The price we pay is that the lineshape is completely changed, the positive central 

The use of sine or cosine functions in FID data processing is an essential tool in 2D NMR. 

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